Pro Football Focus has a piece about NFL quarterback spending and relative value. The conclusion, while not surprising, is sobering: Paying elite quarterbacks big money is a good idea. Paying comparable money for good but not great QBs is a much bigger risk.

This is, of course, the big question when the Vikings signed Kirk Cousins to a three-year, guaranteed $84 million contract.

He was No. 14 in PFF's rankings last season — better than average, but not great. The year before that with Washington he was No. 20. The year before that, he was No. 13.

Where the Vikings were smart was in the length of the deal. If Cousins moves into the top 8-10 of NFL QBs this season, the Vikings should consider an extension.

If 2019 plays out similarly to 2018, the Vikings by PFF logic (and sound logic overall) should be ready to move on with a younger and much cheaper QB after the 2020 season when his deal expires.

Read Michael Rand's blog at startribune.com/randball. michael.rand@startribune.com.