Well first let's look at the Adam Jones contract and see how it would actually compare to Desmond. In Desmond's favor, Jones got an 85.5 / SIX year deal. That's about 14.25 million a year. If we go just by that a 7 year deal for Desmond would be 100 million dollars, rather than 85.5. Prior to the contract year Jones had one good WAR year (4.3 WAR - and I'm using fWAR if that matters to you). Desmond has produced two straight years at least that good, which would also suggest a larger contract.
Against Desmond, Jones' contract only bought out a single arbitration year. There is a sense that arbitration years are worth less, and thus can sometimes have significantly lower payouts than FA years bought up. The Nats would be buying up two arbitration years. Also Desmond will turn 29 (very late) this season. Adam Jones was a couple months from 27 when he signed. You expect age-wise better years from Jones.
That's just a starting point. Really what you want to know is what SSs are being paid now and how does Desmond compare to these shortstops. We're going to look at recent long term deals covering many FA years. Desmonds fWAR (don't concentrate on this as a hard number - just think of it as relative value) for the past two years combined is 10, 5 per year. This is considered his age 28 season for stats purposes.
- There was one big SS contract signed this off-season. Jhonny Peralta signed a 4 year deal for 53 million or an average of 13.25 million per year, covering ages 32-35. He averaged 3.6 WAR in the three years leading up to the deal
- Prior to the 2012 season, Jose Reyes signed a 6 year deal for 106 million or an average of 17.6 million, covering ages 29-34. He was roughly a 5.5 WAR player when healthy but had some injury history
- Prior to 2011, Troy Tulowitzki extended his contract 7 years longer for 134 million, or 19.1 million per year, covering ages 29-35. A 6+ WAR player in a theoretical full season, Tulo has had constant injury woes taking chunks out of his seasons.
- Commenter Todd Boss mentioned I left out Elvis Andrus. 8/120 million (15 per) for a 4 WAR player at time of signing covering years 26-33. Elvis is a doubly unusual case. He had his first full year at such a young age (20) that to cover the usual age-ragne would require a 9-10 year deal, that's why it ends at 33. Also the contract has a player opt out after 4 years. At age 30, which could make it a 4/62 deal. Either way confirms point - good FA SSs are worth at least 14.25 a year.
Even if you want to look at the Simmons deal (7/58, 4.7 WAR last year) as a place to start, Desmond can immediately point to his FA years bought out at 13 and 15 million dollars a year respectively. That's right around the 14.25 we're setting as a base for Ian. The only deal that looks favorable to the Nats is Starlin Casto's where they bought out 3 FA years at 9, 10 and 11 million. Of course at the time Casto was about a 3 WAR player, significantly less valuable than Desmond.The only hope for the Nats is Stephen Drew getting a terrible deal, but again, he's not that comparable, already 31 with a 3.5WAR season last year, preceded by two injury riddled years.
The numbers make it pretty simple. If the Nats offered 7 years at 85-90 they offered under market value for what 7 FA years would bring. Perhaps if you factor in the bought out arbitration years you could justify 7/90 but that's right at the bottom limit of what you could justify. Desmond, is making the right choice. Now he needs to back it up with another good year.