Most 3D rendering software is expensive. I have a copy of Houdini (used to make Toy Story) which retails at $15,000 (of course I didnt pay full price for it). However, there is a program called Maya. They have a free version of the program online, its not a full version but I im pretty sure you will be able to work it for what you want to do.
Maya Learning Edition
Link doesnt work, but just click on downloads and look though the page for the free learning edition.