I guess your best bet would be something like GMax with a suitable plug in for the app you want to make stuff for. GMax is a free, slightly cut-down version of the industry-standard 3D editing software package, 3DSMax. A lot of people use 3DSMax for modding, but I think it is fair to say that many who do will be using a hacked version, because a legit copy of 3DS will set you back several thousand bucks.
As far as I'm aware, you can still download GMax for free from turbosquid, or, failing that, GMax is often bundled with software (such as most current versions of MS Flight Simulator - so you could buy MSFS 2004, i.e. the old version and get GMax for about a tenner if it is still not freely available, check the box to make sure it is included in that version though, and make sure there is a plug-in for what you want to do). GMax comes with comprehensive tutorials, although expect about a two-week learning curve to be able to do stuff reasonably well.
GMax requires plug ins in order to export in formats suitable for various games and sims, but you can usually find these on the net for free.
I did hear something about Maya releasing a chopped down free version of their software, but I've not checked that out.
If you want a really good 3D software package that is very intuitive, another (not free) option would be Animation Master, which is about 200 dollars or so as far as I recall, not sure, I bought it quite a while ago. This software is aimed at producing 3D animations along the lines of Toy Story etc, and is a real bargain considering its capabilities, very easy to use. But aside from its capabilities, it will also export and import .obj files and allow you to edit them.
Then you have things like Blender et al, versions of which you can get for free, but personally, I don't think the interface for it is very intuitive.
Another option is to look out on PC magazine cover disks, where they very often give away older versions of such software packages, look out for back issues which did this, you can usually check this out via the magazine's website and ordewr back copies there.
Chock