I posted a review of Dive Hut, a reputable budget option, in this forum section the other day, and another place or 2 were mentioned in that thread.
In the past, when I've evaluated online offerings for different places, some (WannaDive and Buddy Dive) shops included what amounts to free nitrox upgrade in the basic package deal, whereas Captain Don's at least sometimes did not, so be sure you're comparing apples to apples when you price.
Buddy Dive and Captain Don's are both reputable, and located side-by-side, and have nice housereef dives. I stayed at Buddy's once and liked it.
Richard.