I just bought 500g of yeast on ebay. Cheap as chips. However, if you're just planning on making bread, why not do large quantities no-knead style dough where you leave the dough overnight? I've just made 25 or so 1kg loaves with a friend and she just used one single 10g packet of yeast for the lot! It does mean freezing the bread but it comes out fine (if you have the freezer space).