I have seen several cheap, imported single-action .22 revolvers that sell new for about $150, or used at a pawn shop for $100. They are probably made of inferior metal, poorly-fitted, and inaccurate. I would not expect the gun to shoot to the point-of-aim of the fixed sights. But they should suffice for training purposes, to show how a single-action gun is loaded and unloaded, how to eject the empty cases, etc.
I have fired two such guns. I don't recall the particular brand names, but I think both were made in Italy. They both worked reliably. One was very accurate, the other barely acceptable on accuracy, but both were good enough to plink tin cans with at 20 feet or so.