I want to say that C4D is about $500 educational... not a cheap program, but it's much more accessible and easy to learn than other packages (esp. lightwave and maya).
There are other less powerful but still good packages out there, but C4D, IMHO, is one of the better balances between zero 3D knowledge and lots of it. One of my instructors, who's in the industry, has actually said that he feels C4D is a stronger modeler than Maya, esp. if you don't already have a strong background in it.
Another one to try that is much cheaper is Amorphium pro... which has some neat modeling features, but is pretty bizarre in general. I want to say that costs much much less. Electric Image Universe is available is you buy the 3D toolkit from dvgarage.com (a great place to start learning tips and tricks... plus lots of ways to add subtle details to your scene... mostly through texturing). I've never used that software package, but the site's creator (Alex Lindsay of episode 1 fame) totes it for a lot of reasons, and I certainly won't argue with him (because he's pretty hardcore).