Personally - I feel that even small benthic species of sharks - should have enough room to replica a native type habitat in. For this reason - I don't think commerical built tanks/aquariums are the best way to display them. The largest commerical home aquariums seem to be in the 500-1,500 gallon range - but are usually no more than 4-5 ft wide. And those tanks can be between $2,500-$10,000 each.
Rather the best way - is in custom built aquariums or ponds, are much better suited for sharks - provided that it's adequete keeping the species of which it's designed for.