I have always had good luck with Springfield Armory bbls from Brownells. They drop in and are only about $80.00
A friend put a Storm Lake Machine bbl. in a pistol he built up from parts, it was a much tighter fit and much more accurate, but they are about $150.00 from Brownells, although they come with link, pin & bushing where the Springfields don't.
It all depends on what you want to spend and the performance you want!