I use an Optoma PI500, a 15 incher that was, I believe, $400. It’s really not the best thing in the universe – its pen needs a battery, it doesn’t work in some programs (GIMP being one; I think I heard it doesn’t work with Flash, but I can’t verify that), it has a few calibration quirks, and you can pretty much forget about driver updates. But I still think it was probably worth the money – or it would be if I used it enough. I really suck at using a tablet without a screen, and I don’t have a working scanner (and even if I got one, it wouldn’t be useful for digital drawing/painting, y’know?). Nothing beats drawing right on a display, be it pencil and paper or pen and tablet.
So far I’ve found it easier to work with the mouse for all my 3D stuff, no matter what it is I’m doing. There is an occasional exception where it’d be easier to do something with a tablet, but such exceptions are uncommon for me. I just use the tablet for 2D artwork, but it’s still awesome for that (other than the annoying quirks). But that’s just me… some people find a tablet really useful for 3D.