I would be very hesitant to buy a used lower-priced revolver. The hand, pawl, and cylinder stop are small pieces of metal that wear out or break. Same for the springs. They are not easy to work on. I recently passed up an Italian-made single-action .22 revolver that was offered at a yard sale for $75. The cylinder wouldn't turn, and the seller was saying "it only needed a $3.50 part". H&R revolvers are probably the best of the lower-priced bunch, but I'd check them out carefully before buying. Semi-autos have fewer parts to go wrong, but need attention to the condition of the extractor, ejector, and magazine(s).
I've acquired and repaired a few"junker" guns. It was a good learning experience, and some of them turned out OK, but in the end I opted for newer, better quality firearms. Shooting them is a much more satisfying experience, and I have much more confidence in them. So, if you want to learn about gun repair, buy cheap. If you want to concentrate on shooting, spend more.