As someone who knows this topic from every angle, I thought I might add some insight. We own a storage facility and we own a flea market where we rent booth space to vendors. On the side, we also go to auctions and sell our finds in our store. We charge $1 sq ft +10%. I believe this is the norm for our area (Crystal Coast, NC). A lot of people in our area have tried to open up thrift stores and most of them go under just as quickly. My advice, keep your overhead as low as possible, rent booth space at a thrift store or a table at a flea market and you can also consign the really good pieces, but stay away from getting in to deep (purchasing) unless you have a second income to compensate. If we had only opened a thrift store and didn't have the storage facility to back it up, we would have been out of business already. Retail is a hard business in this economy and there is a lot of competition.
Hope it helps,