There are a good number of 3D printers currently available, from several companies. A couple are in the $500 or so range. Price varies widely, as does the resolution/print quality of the various machines.
And yeah, this'd be a great way to knock out that fleet/horde of miniatures for whatever game you have in mind. Assuming you can afford the printer, software, and materials that is!
The trick is to accurately model whatever you want to print. Of course, we have some modelers here, so if we could get them to make the proper shape files...