Buying a d9h that's been sitting for years

Hi all. Heard on the grapevine of a d9h that's for sale and rang the owner about it. So the back story, guys old man bought it out of the mines, spent almost as much again on the rear end before using. Used it for a while on the farm and cooked it, apparently one of the heads cracked and it lost coolant and overheated. ( you would assume it would most likely happen the other way) anyway a mechanic pulled it down to rebuild it and ended up leaving town and it has never moved since. I have seen this tractor years ago and I know it's been sitting for at least 15 years Mabe longer. That being said what would you say this is worth and would it be viable to fix? Obviously this depends on price and condition just after a few thoughts from people in the know before I go for a look. He is going to do some research about price and get back to me, it might be out of my league to begin with lol.
Ps they have 2? New heads for it aswell.
Cheers all will appreciate any suggestions and advice.

Buying a d9h that's been sitting for years