Start small, $10-20 every payday. Hit the stockup stores like ALDI, rotate your stock and it won't be long until you have a 6 month plus supply of canned and dry goods.

We've never had trouble keeping rice and beans good, but we never bought them by the huge bags, either. Personally I think there's more of a chance of spoilage/infestation of one 50 pound bag than 50 one pound bags you would get at the store.