It's tough to evaluate something that has been stored away for decades. The tractor appears to be a 1979/80/81. It really doesn't matter which one of those years applies because it does not affect the price. On one hand, you could look at what other 200's of the same vintage are selling for and put the price on the high side of that figure. If a nice 222 from 1980 came on Craigslist, the selling price could be as high as $1000.00. The problem with the Seller is that he thinks his tractor is worth a lot more than that because it has been stored away, yes? There's nothing really unique about what's shown in the photo other than condition.
Let's say (for discussion purposes) that he only put 10 hours on it before parking it. Essentially, it's still a new tractor but he isn't going to command $5000.00 for it because it is not a 2011 unit. But for the Buyer who is thinking about buying a new machine, something like this could be a bargain at $2500.00 but only if he intends to keep it for the next 15 years and use it. The cost of ownership over that period would be only $167.00 per year and the tractor would still have residual value to someone else in 2026.
The true test is to put this tractor on e-Bay for 99 cents and no reserve to see what happens. I can tell you right now that the Seller would not be happy with the hammer price. The tractor will be primarily judged by the model year and not by what it would cost to buy something equal in condition. Hopefully for him, it's a 224 because in the HP crazy world we live in, a 220 or 222 would have considerable less appeal to the uninformed.