Buy a 12 pack, and aim to make it last a week (and if you run out before then, too bad). If you can manage that, maybe try and make the next one last 10 days or even a fortnight. If you can get a 12 pack of beer to last two weeks (and it'll probably be easier the longer you do it), then that's your beer expenses cut :)
I've started buying the beers from Aldi, and find that they're usually pretty good, and much cheaper than the big brands, and way cheaper than the micro brews (which are often $20 for a six pack here, beer prices here are crazy).