I'll just post something I wrote on the BGS forums:
You can make prints of some posters yourself.
For instance, the Red Menace poster, printed at 200 DPI is a 65x31 cm poster with acceptable quality. You can go lower, at 150 DPI it gives you 87x41cm (34x16 inches). Depends on the quality you want.
There are also five other print-ready files: Courage Today, Victory Tomorrow!, We'll Be There, Chryslus ad 1, Chryslus ad 2 and Nuka Break.
Here's a calculator to figure out the sizes,
If you want to make REALLY high resolution posters, consider using Rasterbator to create a rasterized, tiled version of your poster. It's quite awesome.
That said, I think that ultimately the cheapest option is screen printing your T-shirts on your own. :tongue: