A 480-600 gallon aquarium(8' long x 4' wide x 2-2.5' deep) may be fine for either a gray or brown smoothhound for about 2 years(at which time they will be about 25-30") or so - but not much long than that. They will outgrow it.
A better alternative to the 480-600 gallon aquarium is to build your own shark pond. A 480-600 gal. glass tank will cost about 2,000 bucks (unless you build it your self). To build your shark pond(say 12' x 6' x 3' or about 1500-1600 gallons) will run you about $500 in materials.
If you were to do everything your self, you may spend about 2,000-3,000 bucks on the complete system - pond, sand, salt, filtration & LR. Maybe more it you really want added pleasure to view the shark from the side of the tank.
And if that sounds a bit huge - then try to figure keeping a shark like a blacktip reef or bonnethead.