Buying cheap to fix, good idea?

Don't buy a junker, go for one that looks good to start with; check it out carefully and if everything is good make the purchase. Most times a private owner who has a reasonably good looking outfit also took care of the maintenance. If things look a little worse for wear, many other things that aren't readily apparent are probably going to be problematic too such as the furnace, fridge, AC, engine, brakes, etc.