If nothing else, the 2017 NFL season was a reminder that backup quarterback might be, as former Giants and Browns executive Ernie Accorsi used to say, a team's second-most important position.

Of course, the football gods have sucker punched Vikings General Manager Rick Spielman enough the past two years that he understands this as well as any decisionmaker in the league.

In fact, Spielman hasn't had a Plan A at quarterback make it past Week 1 since 2015.

So perhaps it's fitting that Spielman spent Wednesday trading for Denver's Trevor Siemian, a $1.9 million backup quarterback, before officially pouring a guaranteed $84 million into Kirk Cousins, his new starting quarterback.

That's quite a day considering it was only a couple of days ago that Kyle Sloter, a second-year pro with no experience, was the only quarterback on a team built to contend for Super Bowl LIII.

Siemian is only 26, but he's experienced with 24 starts (13-11) while still being affordable in the last year of his rookie contract. The Vikings also get a seventh-round draft pick this year for a fifth-round pick next year.

Spielman's options via free agency were more experienced, but certainly would have been more expensive with no guarantee of being any better than Siemian.

Trevor Siemian

As the signing period began Wednesday, there were 22 unrestricted free-agent quarterbacks still available out of an original pool of 30. Most, if not all, of them are backup-caliber players.

Sixteen of them have 16 or more regular-season starts. Former Viking Matt Cassel, 35, has the most at 81 (36-45, including 4-5 in two years as a Viking).

Mark Sanchez is next with 72 starts, but his 37-35 record and 4-2 playoff mark were pretty much proven to be fool's gold long ago. Vikings offensive coordinator John DeFilippo, who was Sanchez's quarterbacks coach with the Jets in 2009, had a say in the Vikings' decision Wednesday.

Other options: Drew Stanton (11-6), Chad Henne (18-35), Derek Anderson (20-27), Matt Moore (15-15), Geno Smith (12-19), Kellen Clemens (8-13), Blaine Gabbert (11-34), Brock Osweiler (13-12), E.J. Manuel (6-12) and, well, you get the idea.

Not exactly good investments.

The Bears gave Chase Daniel a two-year, $10 million deal to back up Mitch Trubisky. The Cardinals gave Mike Glennon a two-year, $8 million deal to back up Sam Bradford.

And the Jets, who probably will draft a quarterback in the first round, gave one-year deals of $10 million to Josh McCown and $5 million to Teddy Bridgewater.

At the scouting combine in February, Chargers General Manager Tom Telesco was asked if the 2017 season would jack up the price tag for backup quarterbacks.

"That's a good point," he said.

Indeed. The NFC Championship Game featured a battle between Philly's Nick Foles and Minny's Case Keenum. Foles won and went on to outplay and beat Tom Brady in Super Bowl LII.

Today, Foles is Carson Wentz's backup, while Keenum is the presumed starter in Denver.

"You've got to have a good [backup] to win, and they're hard to find," Telesco said. "They're an asset. The Eagles did a great job having a quarterback like Nick Foles come in and play the way he did.

"We all try to do that. It's hard to do. The supply isn't always as big as you'd like."

Obviously, Spielman felt the UFA supply was bone dry. So he didn't waste any time executing Plan B for his Plan B at a price that's more compatible financially with keeping the strength of the entire team intact.

And it's that team strength that catapulted the Vikings to 13 victories, Keenum to an $18 million-a-year salary and offensive coordinator Pat Shurmur to head coach of the New York Giants.

"We've had to deal with a lot of adversity at that position, and we've been very aggressive," Spielman said at the combine. "I also think when you look at our situation and even Philadelphia's situation, we have a pretty strong roster. … You're hoping your roster is strong enough where you don't have to put everything on that backup quarterback."

Mark Craig is an NFL and Vikings Insider. Twitter: @MarkCraigNFL. E-mail: mccraig@startibune.com.