Lunchtime had arrived in the Caribbean bay, and the diners came from on high, pelicans wheeling and turning overhead like ungainly adolescents. One by one, they caught sight of a target in the water below, snapped their great wings in close and dropped, sleek missiles slamming into the cornflower blue waters near my head.

Their prey was mine, too, but what they ate I merely watched, mesmerized by the colorful fish darting in and out of the coral reef. The odd-looking fairy basslet — its back half yellow and its front a royal purple — swam into view, then tucked behind a waving stand of purple fan coral. Swirling nearby were fish so numerous it was hard to keep track: blue tang, stoplight parrotfish, porkfish, yellow goatfish, grunt, wrasse, bar jack, sergeant major, schoolmaster snapper.

Out of the corner of my eye I caught a silver flash and turned just as a large Caribbean game fish known as a permit, this one the size of a coffee table, zoomed in at me, banked right and shot away into darkness.

Heart pounding, I glanced back toward my wife and two sons. Snorkels on and masks in the water, they were each in their own trance and hadn’t noticed my close encounter.

The permit had shocked me, and for a few moments I floated, wondering how this had come to be: my middle-class family with a lean bank account was snorkeling along the coast of St. John in the U.S. Virgin Islands, the onetime playground of the Rockefeller family. On this stunning, sun-drenched day, the four of us non-Rockefellers were the only people in sight.

Timing helped. We visited during the tail end of Hurricane season in early November, when prices are generally lower. We ran the risk of a trip curtailed by bad weather, and for our first day and a half there, heavy rains and gray skies prevailed. We were grumpy, but locals praised the rainfall. It fills the cisterns that many people rely on for drinking and bathing water.

We left the snorkels packed and took a rainy but scenic hike across a portion of the 20-square-mile island. After that spell of cistern weather, the winds picked up and cleared the sky of clouds. We didn’t see rain again until the drive to the airport on the day we left.

Our affordable Caribbean vacation is also a tale of travel hacking. Those Rockefellers played a role, too, which I’ll get to in a minute.

Getting into the Spirit

My wife, Molly, and I have always been travelers, and before our two sons came along we saw much of the world. Family life slowed us down considerably, and except for a few early tries at vacations in New York and Los Angeles with our first son, by last summer we hadn’t flown anywhere together in nearly a decade.

Then last year, struck by some ancient wanderlust, Molly applied for a Spirit Airlines credit card. The card promised a few thousand miles in the Spirit Airlines rewards program just for signing up. In addition, she joined Spirit’s “$9 Fare Club,” which promised even more deals for an annual fee of $60 the first year and $70 every year after that.

To her astonishment, Molly soon learned that she had enough miles to fly the entire family to Florida for a cheap winter getaway, provided that we headed down in the offseason. The cost was so low, about $400 for everyone, that she started looking through the Spirit website to see where else she could take us. And that’s how, on a steamy July night, we ended up booking travel to St. Thomas (a cheap ferry would get us to St. John) for the two of us and our two preteen boys for $1,000.

There are drawbacks to flying on a discount airline. The planes have less legroom than more expensive flights. There’s no free Coke or peanuts. And there’s a fee for any bag beyond the one small “personal item” the airline allows for free. For a family like ours, we could skip the peanuts if it meant vacationing in the Caribbean.

Then again, this was just the flight to St. Thomas, and we would need to take a ferry ($50 round trip for everyone if we were in a rented car) to get to St. John.

We also needed a place to stay. Many of the hotels on St. John offer the kind of lodging you might expect on an exquisite Caribbean island, meaning expensive. On one listing of the 32 best values in the Caribbean, St. John doesn’t even make the list.

This is the Rockefeller portion of our tale: In 1956, the financier, businessman and third-generation Rockefeller, Laurance, donated his significant land holdings on St. John to the U.S. National Park Service. Rockefeller was eventually awarded the Congressional Gold Medal for his conservation work, and today Virgin Islands National Park covers about 60 percent of the island’s 20 square miles.

Not only has the national park designation kept the island largely undeveloped, but the park service runs a campground at a spot known as Cinnamon Bay. True to Rockefeller’s vision that the spectacular beauty of St. John would be enjoyed by many, the campground sits on what is arguably the island’s best beach. With white sand, rocky outcroppings ringed by coral reefs and leafy green islands on the horizon, Cinnamon Bay typically shows up on Internet lists of the world’s most desirable beaches. We stayed for just $57 a night.

The campground has three types of lodging available, from concrete “cottages” that started at $121 a night for a family of four, to canvas-walled platform tents for $107, to bare sites, which is what we signed up for. The trick to a bare site, of course, is that you need to pack your own tent and cooking gear. And if you’re flying on Spirit Airlines, every bag means more money spent.

To keep our airfare affordable, we packed light, but brought snorkel gear. This was the Caribbean, after all, and most of the travel sites I visited said you don’t need to bring much to St. John. A camping bag included a family-sized tent, a single-burner propane stove (without the propane, since it’s not allowed on the plane) and two queen-sized air mattresses. Another bag held food, including noodles, instant meals and dried fruit — which we could bring because the islands are part of the U.S. The boys wore life jackets onto the plane, to save room in our cramped bags.

Our final big-ticket item was transportation on the island. We decided to rent a vehicle rather than use the island taxis, which are plentiful but somewhat expensive for a family of four.

We’d heard that roads could be steep, Jeeps are better than cars, and bicycling was not at all advisable. Still, because a car was significantly cheaper than a Jeep, we expected to rent one for the week. But when we arrived at my budget-minded car rental place — a company we chose despite online travel forums littered with horror stories about its service ­— we saw a long line of passengers waiting at an ominously empty counter.

That’s when I called a highly recommended place a few miles from the St. Thomas airport and paid $600 for a four-door Jeep for six days. That last-minute decision proved a good one.

Exploring by Jeep

Most days, after a breakfast overlooking the beach, we hopped in the Jeep to explore.

One day, we zipped up the tent, loaded the Jeep with snorkeling gear, and set out to the far east end of the island for lunch at a remote spot that served beans and rice, conch fritters and something called a Johnnycake.

True to the warnings, the few roads that exist on St. John wind up and over steep mountainsides at pitches that would be nearly undrivable in a small car. That’s why the speed limit everywhere on the island is a mere 20 miles per hour. Not that we were in a hurry. The slow pace gave us more time to gawk at the feral hogs. Pink, huge, and not at all what we were expecting in the Caribbean, the pigs are descendants of the animals brought over from Europe by Christopher Columbus (credited with naming the Virgin Islands) and the Danish farmers who established sugar plantations on St. John. We only saw a few, but they made an impression.

At Vie’s Snack Shack, the Johnnycake turned out to be reminiscent of a doughnut, and with or without the honey Vie recommends for it, the caky goodness makes a great complement to her version of rice and beans. As we ate at the plastic tables set out for diners, we listened as other visitors talked about the island’s best beaches.

Armed with their recommendations, we made a short drive to Haulover Beach. We hiked along a footpath through dense vegetation, stopping along the way to watch hermit crabs somehow navigate their way over tree roots and rocks, hauling big shells on their back. We were stopped short by the sight of one crab, the size of my son’s fist, perched 6 feet up in the crook of a tree branch.

The beach, far from St. John’s largest port in Cruz Bay, was nearly empty. We slipped into the water and swam a short distance to a stand of elkhorn and brain coral, fast moving fish and one pink jellyfish — a Virgin Islands menagerie.

Most nights, we headed into Cruz Bay for after-dinner ice cream or a Dark and Stormy, a local drink made of black rum and ginger beer. We saw local men playing chess in the town’s main square. Jazz music — a flute and a guitar — streamed out the open windows of a nearby restaurant.

Some of the bars had a distinctly spring break feel to them, but for a Caribbean town with a heavy tourist trade, Cruz Bay managed to feel more homey and friendly than some of what we had seen on neighboring St. Thomas.

As we walked through town we passed the local community center. Two classes were underway, yoga and steel drumming. In the drumming class, local kids dutifully pounded away at the musical drums as their glum instructor rapped out a beat. He stopped them frequently, and if someone continued to play when he demanded silence, he threw an exasperated look their way. Even paradise has its downside.

The kids started over and between breaks we learned they were practicing for an upcoming festival. We would be long gone by the time they performed, but the song they played that night still resounds in my head when I think of Cruz Bay.

The performance, like much of what we enjoyed most on St. John, was free. We’d needed to travel inexpensively, but there were many moments — my son and I pausing in our breakfast cooking to watch a flying fish skip across Cinnamon Bay, or my wife and I marveling as our sons took to the ocean with a confidence we didn’t know they had — we knew this trip was worth every penny.