It's a dirty little secret in the airfare search business, but consumers waste millions of dollars by overspending on airfare because airfare search technology is far from perfect.

We were reminded of this again when we recently noticed a classic fare war between American and United on routes from each other's hubs (Chicago, Dallas, Denver, Miami, Washington) to Honolulu. (Both airlines reduced fares to about $420 round-trip including tax, with virtually no restrictions.)

But what if you actually wanted to go to Kona, Hawaii, rather than Honolulu, from, say, Miami? Well, all the usual airfare search suspects would have told you that the cheapest way to get there would cost you $688 round-trip including tax. (We used travel dates in October in our sample query.) Savvy traveler that you are, you know that doesn't make sense. Surely it doesn't cost $268, the difference between the two fares, to travel round-trip inter-island.

You can fly between Honolulu and Kona almost year-round for $150 round-trip, including tax. So most people end up paying $118 more than they should. If you're a family of four or a group, that price difference can add up.

The issue here is that no current airfare search technology (and that includes Kayak, Travelocity, Orbitz, you name it) can figure out fares this way. There are thousands of route combinations where buying two separate fares will save you money.

Flying from New York to Eleuthera in the Bahamas? Try JetBlue to Nassau and then Nassau to Governors Harbour on Bahamasair, and you might save hundreds. Flying to Asia? You might find a Web-only deal on Singaporeair.com to Singapore and then hop on a next-to-nothing flight to Phuket via AirAsia.com (at this writing, flights from Singapore to Thailand are running about $36).

The good news is that airfare geeks are working on this. But until airfare search reaches the next level, you'll have to use your noggin. When an airfare you see just doesn't make sense, make sure you're getting the lowest fares available by combining flights on different airlines. That's what a good travel agent used to do, but the Internet has put many of them out of business.