Saltwater
Cheapest synthetic water is Pacific Reef in Fountain Valley or Orange. It's 69cents a gallon but you get what you pay for. The params are always off PH 7.8 etc...Best synthetic water is at Ali's Amazing Aquariums in Orange but pricey at $1.00 a gallon. Cheapest Catalina natural ocean water at Seaside in Huntington Beach for 39cents a gallon. Hope that helps. This is all assuming you're in OC.