There are lots and lots of 3D programs on the market, the most powerfull are usually said to be 3D Studio MAX, Lightwave, MAYA and Softimage. Not sure of the prices, you can't afford any of them though

3D Studio MAX is some 3500 USD, Lightwave a bit cheaper I think, MAYA too, Softimage is probarly around 10,000 US dollars. (guessing from what I've "heard" before).
There are also quite a few free ones and quite a few pretty cheap ones.
AutoCad 3D is quite often used to make modells, there are quite a few who use Autocad to make plane modells for the Targetware flight engine right now. Autocad 3D is fairly cheap, bellow $100 I THINK.
There is a FREE Version of MAYA, however every picture you make there is Water Marked.
MAYA To the right is a small link "MAYA Personal Learning Edition".
Another really good program is GMAX, it's a free version of 3D Studio MAX specially designed for Gamers. The company that wishes to support GMAX modells in their game must pay a large ammount of money, one time. Then, after 2 years they must pay more and contineu every year (what I've heard). GMAX can officially only be used for games that Support it, currently MS FLight Sim 2002 Quake 3 and a few more, however, there are ways around it that are legal and any modells you make in it can be converted to other 3D Formats. If you decide to go with GMAX I'll tell you how to convert and export etc.
GMAX is a really good powerfull program, that it is free only makes it so much sweeter.
GMAX Last, there is a program called "NENDO", pretty powerfull, looking at things that people have made you can make very nice things in it. It costs $99 but a Demo is available for download free.
NENDO There is also another program, forgot the name, it was in some posts ago on AH BBS. See if anyone reads this and can add it to the list.
I haven't modelled for long my self (haven't done it for like 2 weeks now either) so just learning it too. Worth the time spent on it though, very fun.