I realize that this is a bit of old topic now.
But allow me to answer some of the questions that jr had asked.
First off - Blacktip reef sharks require at least(18' diameter pool) 7,500 gallons(not the 5,000 - often reported). They are very hardy, but highly active tropical sharks - tend to prefer water temps in the range of 75-84 F. They regularly sale for $900-1,500 each.
The best free-swimming species for a novice keeper is the smoothhounds all of which average about 3-4' in length. The Grey & Browns are cooler water species(requiring a chiller) that prefer water temps around 60-70F. A better alternative to these is the Atlantic or Dusky Smoothhound, which perfers water temps around 68-78F. The Greys & Browns sale for around $150-200 each. The Atlantic(Dusky) sales for around $250 each. These sharks can get by in a shark pool as small as 1700-2500 gallons(10-12ft diameter).
The Leopard shark is a cool water species with similar requirements to the Grey & Brown Smoothhounds. They also grow to about 6 ft. in length, and are found in the market at 3 ft(no smaller). Also the Leopard requires a tank that is at least 5,000 gallons.
Also the Atlantic Sharpnose is a good alternative to the Blacktip Reef, as they are smaller & adapt very well to captivity. They look like mini-blue sharks(except for that they are gray in color). They stay to roughly the same size(3-4 ft) as the smoothhounds. But they are more active than the smoothhounds. Like the Blacktip Reefs - they are a warm water species - preferring water temps around 77-86F. They require a pool that is at least 15' diameter(4,000 gallons) for the adults. The Sharpnose regular sale for about $350-600 a piece.
The Bonnetheads are actually less hardy than all of the above species. They are really a species best left for experienced shark keepers. Although their size (roughly 4-5' long) is good for larger shark pools. They tend to be finicky feeders. They require a pool that is at least 15' in diameter(4,000 gallons). They regularly sale for between 700-1,200 each.
Still there are better choices of aquarium sharks for novice keepers. The Bamboos, Coral catsharks, Epaulettes, & Horn sharks are all much better choices and generally easier to keep as they are less-active and require smaller tanks sizes (usually between 150-400 gallons).
I do recommend you get a copy of Scott Michael's book Aquarium Sharks & Rays, as it will greatly help to answer most of your questions in keeping sharks as a potential keeper.