Keystone is the cheapest i've seen in Vegas, it's about $5.00 for a case of 12. Tastes like shit though.
Holy shit, that's some cheap beer. The cheapest beer that's readily available in Australia is usually some imported German shit like Oettinger which can get as cheap as $10 a 6-pack when it's on special. The cheapest beer WORTH drinking though is probably Boag's Draught or Melbourne Bitter (but never Victoria Bitter, fuck that).
Tesco Value Lager 2% 4X440ml - Groceries - Tesco Groceries 81p for 4 cans! Or about 1 dollar 29 cents for 4 cans! Not too sure on the taste!