When I first started I used treated tap city water. It's not as good as RODI but it worked. I've run RODI as a temporary setup as well when I didn't have a place to set it up. I don't think .50 a gal is too much, grocery store distilled is .80, plus if you visit often you'll have a good relationship with them which may lead to better deals, or at the very least, good insight into the hobby.