That tractor appears to be a 1980 model in average condition with no special optional equipment. If it were in good running condition and the engine did not have any major problems then it might be worth $800 but not as a non-running tractor. It undoubtedly has a broken rod and it is possible that it could be repaired for a couple hundred dollars in parts but it may also need a lot more and you won't know until you tear it apart. If it is necessary to do a total rebuild then you're looking at close to $1000 in parts alone if you do it yourself. A good running used engine might cost you $400-500 so my calculation is that the tractor is worth a max of $300-400. If you are not able to do the engine work yourself I would pass on this.