If it has been well maintained that is a decent deal. If it hasn't, run away. If it's in good shape it will outperform anything else you can get for that money.
My experience is that parts are widely available from online dealers, and relatively inexpensive. This is especially true of the 200 series.
This was not an expensive tractor when it was new, I recall it was around $3500 for the bare tractor. Many were sold to inexperienced users who didn't know the importance of oil changes, air filters or coolant. These tractors are heavy and tough, but can be damaged quickly if run without an air filter or proper lubrication. In particular, if allowed to overheat the head gaskets blow quickly. On some versions the radiators were positioned so they were prone to clogging with chaff and they would overheat easily. Once the head gasket is blown the oil can get contaminated and other engine parts can fail.
Do not buy this tractor if it doesn't start easily and run smoothly, or if all the cylinders don't fire. We get a lot of people here who buy Jinmas that are running rough and they get them home and open them up and find out the head gasket is shot. For more detail, see my post #6 on this thread:
http://www.tractorbynet.com/forums/chinese-tractors/287274-jinma-200-hard-starts.html
A Jinma with a blown head gasket is actually a good project, they're not that hard to fix. I just wouldn't pay any money for it.
By modern standards the weatherproofing on these tractors is poor. They need to be stored indoors. Do not buy it if it looks like it was stored outdoors.