I'd say your best bet is finding something in the classifieds or a friend with a shotgun. If you aren't fortunate enough to have a friend with a gun for sale or don't know what to look for with used guns some of the bigger retailers usually have decent sales. As evil as places like Walmart or Big5 might be they are cheap. That said all the shops I've been to have fairly good prices and customer service. I haven't been impressed with the prices I've seen online since most things I've bought where 10-20%(or more) than what I paid for them(and that was before shipping and transfer fees).