One of my favorite combinations is D GA CGA and Metasequoia (all free depending on which versions you get.) D GA CGA is a dirt simple to use 3D modelling tool based on a parts bin metaphor. Metaseqouia or Milkshape (shareware) can be used to convert the D GA models into a game mesh.
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TAZ
I have been using AC3D because it is easy and relatively cheap, you can download a 14 day trial. You can also look on TurboSquid and see if any of the models you need are already avaiable for free/cheap.