Bryce 5.5 is free as well as I am thinking you can get Auto Cad Light for free the trialversions or something like that...Bryce you can import the .obj's and manipulate them but out of thin air not sure...
Blender may help you out...haven't gotinto using it but this may help ya..
http://www.blender.org/
a free 3d program from microsoft....yep just tested it out...this is one cool ..FREE 3D program...enjoy...can import/export .obj's