Depends what brand of salt you are looking for, but if you don't mind drivng to the East end of Pasadena then Pasadena Tropical Fish has buckets and boxes of Ocean Pure at a decent price.
In fact if you want to try it out first, I have 2 sealed bags of Ocean Pure that will make up 50 gallons each. I just switched to Ocean Pure Pro so I'd be willing to part with these 2 bags. Ocean Pure (regular) is identical to the Pro version except lighter on the magnesium.