Personally, I would not buy it at that price. Check Ebay for comparative prices. Check for parts availability. They do look well built.
I would spend that much on a 300 or 400 series John Deere tho...
You could easily spend $750+ in parts. No telling what labor will be.
I bought a 1995 Exmark 0 turn with a blown engine for $500. I did spend $400 for parts rebuilding it. Another $300 repairing minor things. The previous owner cranked the Kohler engine while the back case half was off. I think something got bent or something. It sounds like a rod bearing knocking but everything is tight inside. It might be the exhaust and thin muffler? Anyway, I am happy with it and ready to find another engine if this one shells out. 2 summers out of it so far.