Rhino: $164 (only one I found with a site license: $817--kind of interesting
that you can get a site license for Rhino cheaper than one copy of 3D Studio
3D Studio Max: $849
3D Studio Max has very specific computer requirements, so if you consider
it, be sure to check them out first.
The one with the most positive user feedback seems to be Rhino, as everybody
comments on its easy learning curve.