They are rare, but I think there are some older small tractors that might fill most of Pele's needs, and come within, or close to, his budget. How about the Bolens/Iseki tractors, or the older, smaller Mitsubishi Satoh tractors? I believe there were some Simplicity garden tractors that took a loader. Aren't there also some early small Kubotas and Yanmars that might be in the ballpark? Someone also mentioned Case/Ingersoll. Those were very rugged small tractors.
Pele - Don't give up easily. Check all the sources you can for older, smaller bargain tractors. You may find something that has lived an easy life, and has plenty of wear left, in your price range. On the older machines, you will likely have to do your own mechanic work, and finding parts will be a challenge. There are plenty of guys that do that as a hobby.
Also, if you haven't already, scout through some of the other sections of TBN for information on the tractors that I and others have mentioned.
Good luck in your quest!