As I wondered how to start yet another conversation about the most important contract the Redskins will negotiate in recent memory, I found this link to a Spotrac page taking a stab at Kirk's market value (h/t to Ed Valentine).
Using Jay Cutler, Andy Dalton, Ryan Tannehill and Matt Ryan as comparable players (this is your first chance to quibble with underlying assumptions), Spotrac adjusted their contracts as if Cousins signed that average deal at his current age (27 years old). The next step involves some wonkiness, and I have zero intention of turning this post into a post-graduate mathematical dissertation. Basically, Spotrac compared the statistical performances of each player in the two years prior to signing their deals.
If your name is McLovin, and you see that your guy just had a year that puts him ahead of all of these guys statistically in the above analysis, you might wince just a little, because it pretty much translates directly into dollars.
As you all know, I freaking love talking about this stuff. Luckily for me and others like me, talking about Kirk Cousins' contract has--at least not yet--not gotten old. The final analysis takes into consideration the percentage change in stats between Cousins and the above passers--and Cousins' 2015 shows a net positive change in each category they list (Pass yds, TD, INT, Comp % and passer rating).
Bottom line (and check out the site for the complete view): Kirk Cousins' calculated market value is around four years at $82 million. I think that is within the range of the majority of the answers we have each suggested in various conversations on this site so far (well, not including ih8's offer of unlimited sleepovers at his house and all the shoulder rubs he can handle).