For any info on keeping sharks or rays, I'd recommend you make your way over to the MFK (monsterfishkeeprs) website. Read up in the marine sharks/rays section. As you'll come to learn, 400-500 gallons is the minimum recommended tank size for the
smallest of species of sharks (this advice will come from actual experience over there, as a lot of the guys over there have been keeping elasmo's for years). And, if you're on a budget, take the idea of having a shark or ray, and throw it out of your head. I hate to discourage you, but sharks/rays can't be kept
properly on a budget. Aside from the usually massive start-up costs, you have to be willing to dedicate 10-12 hours a week to these animals (feeding, observing swim patterns, disease treatment, shopping for fresh food). It's not an undertaking I'd recommend to lightly to even moderately experienced aquarium keepers.
Greg, Frank, and myself have given you many recommendations to fill your tank with unique and interesting livestock. Start there. Then, when you have lots of time and money down the road, decide to make that jump to keeping "monsters"
Also, the tank recommendations from LA or BZ or whoever need to be taken with a grain of sand. For example, at one point, LA's website claimed you could keep Smoothhound sharks in a 180g tank.... 180 isn't even large enough to comfortably house a juvie (800 gallons recommended). These sharks require around 2500 minimum gallons to be happy for life. A far cry from 180.