I think it depends on your expectations. If you're buying it for occassional use and not in need of 4WD traction and not worried about a rollover, it might make a good machine. I wouldn't pay more than $2,000 for it since parts are scarce, if not impossible and one major failure could reder most of the machine useless.
Although A/C made great equipment in its' day, they are not considered "a backhoe to have".