Wally, that ultimately is going to be all your call. Would you be reducing your selling price because of it? I don't believe the Gildan's will command as high a dollar as the AA...
A thought: Did you show the manager the shirt/design on an AA shirt? That may be part of what he liked about your product. If he allows you to set up in the bar, it's a reflection on him as well, if he liked your AA shirts, and you go in with Gildan's, it may change the overall sense of what he thought you'd be selling. Ya know?
Second, do you want your product on AA or Gildan's? It's your name and design on the shirt. Since you originally picked AA shirts for you designs once... I'm thinking that is your tell tale sign already... you picked AA over the others in the past....
If you go with Gildans type of shirt, I would suggest that you don't put any of your designs that go on the AA shirts onto the Gildan's.. do seperate designs for the Gildan's, this way the folks who pay for the AA shirts aren't wearing the same design as folks who pay for the cheaper Gildan's shirts... there can be a distinction...
It's a shame to let money dictate your product integrity.. I think you have to stand by your product, even if it means having a garage sale to be able to buy the additional AA shirts you need... once you are up and running in this spot, you will likely make the money to roll back into AA stock for future supplies...
You only get one chance to make a great first impression...
From American Apparel to Hanes, Gildan etc... 
