I'd say give half of the shirts away for free and sell the other half for $10. People will think you're a nice guy(which I'm sure you are anyways) for giving out a shirt, and then recommend people to your brewery. The other half of the people will think shelling out $10 for a shirt is dirt cheap, buy them, and you'll have lots of people promoting your brand.
If you bought 50 shirts at $10/per and give half away and sell the others for the $10, it basically cost you $250 for advertising. Can't think of any other advertising that's that cheap and will get you face to face with 50 potential clients.