Don't know about the U.S.A., but here in the UK, even reproduction, or very worn modern ex-military kit is not cheap. Replica weapons, inert, non-firing, are difficult here these days, but when they were available, something like a Thompson would be around the $400 to $500 mark - if your lucky!
For period costume and equipment, if you don't want to use re-enactment groups, then Biker Babe's suggestion is probably the better option - hire from theatrical/film/TV costume agents.