You don''t need a 3D modeler for 2D graphics, unless it is prerenderd 3D->2D sprites. You could start out like that. But if you insist on a 3D package, the cheapest you can get is truespace 1.0, it was released free of charge. They want to hook you on thier package so you buy the newest one.

There are a couple other free-ware packages out there but I can''t remember the names off the top of my head. Hope this helps.

TrueSpace 1.x - Free
Animation Master - Cheap, last time I looked it was $199 - and this is a really good package mind you!
Nendo - $99, this is a modeler ONLY! Guess you could use it in conjunction with TrueSpace for a really cheap package with a good modeler...

Those are the cheap choices I know of, ofcourse there are also modelers available that are specific to some games (like Hlaf-Life and Quake II modelers), you could go that way aswell...

If you only want to make a few low poly models I''d go to PlanetQuake.com and search for game-specific modelers there. If you want to get into 3D in general I''d recommend buying Animation Master (until you can afford Lightwave 3D . The cheap alternative would be TrueSpace 1.x, perhaps together with Nendo (Nendo is a very well suited for low poly and organic modeling)