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.
"If God wanted us to filter our beer, he wouldn't have given us livers."