I've been pretty luck to either find non-rBGH milk that is not the pricey-pricey organic kind (usually from local dairy farms). And one of our grocery chains (Stop and Shop) has its own line of organic products that are cheaper than, say, that Laughing Cow kind that is wicked expensive. I think the store organic costs about 60¢ more than the store brand regular milk.

Good luck with the Costco. We have that here but I've never been in one.