– Rick Spielman sat on a golf cart at Vikings training camp one day last week and sounded like a homeowner who just recently upgraded his theater room, purchased new stainless steel appliances for the kitchen and added an expensive patio set to the backyard.

“You know that eventually you have to pay the credit card,” Spielman said.

The bill has come due for the Vikings general manager in constructing a top-five defense mostly with homegrown, ascending talent. Spielman is handing out lucrative contract extensions like a game-show host gives away prizes.

Spin the wheel to see who’s next.

“I’d rather have that than …,” Spielman said.

He didn’t finish the sentence because he didn’t need to. The Vikings are discovering the cost of business when a core group of players reach Pro Bowl status at the same time and deserve new contracts that reflect their value.

In the past 15 months, Spielman has authorized $135 million in guaranteed money to lock up four key members of Mike Zimmer’s defense: safety Harrison Smith, defensive end Everson Griffen, cornerback Xavier Rhodes and nose tackle Linval Joseph.

All four of those players rank among the best in the NFL at their respective positions. All four are between the ages of 27 and 29 — prime earning potential for players of a certain status.

While the ceiling for the Vikings offense remains a mystery with lots of unanswered questions, their defense looks top shelf — on paper and in paychecks.

“No matter what we’re getting paid, what we want to do on the field is what drives us,” Smith said. “The other [contract] stuff is obviously great and you want that for everybody. But that’s a byproduct of playing well.”

Keeping that defensive nucleus intact is vital to Zimmer’s masterplan, and Spielman isn’t done writing big checks. Anthony Barr, Eric Kendricks and Danielle Hunter are on deck. They won’t come cheap, either.

Rob Brzezinski, the Vikings’ salary cap guru, might earn team MVP honors the next few years by figuring out how to make all of these megadeals mesh without losing any core players.

“This has been pretty unique,” Spielman said.

The Vikings knew this splurge was coming. They saw the development of their young defensive players and realized their contract expectations would be significant.

Spielman said planning began last offseason when the team made a number of roster decisions — specifically not re-signing some veteran backups — to provide cap flexibility. Spielman also broke from organizational philosophy of waiting until the final year of a player’s contract before giving an extension. Both Griffen and Joseph had multiple years remaining on their deals.

“We want to reward our players and give them what they deserve,” Spielman said, “but we also have to be smart with how we handle it from our business principles.”

Spielman said he expects to avoid what he described as “cap jail” — unable to sign a core player because they have overextended themselves with other contracts.

Spielman and Brzezinski have their work cut out because they have other areas of importance. You know, like offense. There’s this little matter at quarterback to be addressed next offseason.

“That’s all preplanned as well,” Spielman said.

He won’t divulge his plan. But Spielman said his staff is prepared for upcoming big-ticket contracts.

The money committed to the defense should keep that core together for the next five years. The offense has to start pulling its weight if the Vikings want to become serious championship contenders. But Zimmer’s defense should challenge for league best this season.

“It’s easy to get ahead of yourself when you look around and say, ‘We’ve got so-and-so here and so-and-so here,’” Smith said. “Everything always looks great on paper. But all that matters is what you do on game day.”

That’s true, but big contracts create big expectations. The Vikings have shelled out a lot of money to their defense. Their best players are either in their prime or have shown star potential. Zimmer’s scheme maximizes their individual talents.

That unit looks rock-solid, present and future. Now about the offense …