shucks - at this level of bike it is just not worth the bang for the buck to replace frames. performance bike sells their branded frames for $100 but i don't know how good / bad that is. i was going to suggest surly frame but at $400 that probably costs more than the bike.

my suggestion is (1) get a longer stem, angle it down, move your seat all the way back and try to make your current bike fit. that's how i like my set up too btw although of course not everyone is like me. and it is often said it is easier to make a small bike "large" then the other way around. (2) if you've really tried that and still not possible then consider selling the bike and getting a new one (3) perhaps most convenient, return the bike to the shop if it has been only 30 days or less. kindly tell them it is not the right size.