The price can very for used tractors. You have to take in to consideration the size, the age, does it have problem and location. You first must know what you want the find one that is in quality condition and a good price.
The short answer is it depends. The fee can vary greatly depending on where you get it done and what the negotiated cost is with your insurance company. In most cases a hospital will charge you more...
They varied by brand and size, but most that I've seen prices for were in the $500 to $900 price range. It seems to me that a Farmall F-20 for instance was $695 if I remember right.