Okay realistically... the fisheye is crazy. Also whoever suggested the 16-35mm Canon is WAY above the price range here.
If I were you, I'd find a nice used rebel body of some level (I have a 400D, these are generally sold in excellent condition for around $200). Take your extra $800, and search for the Canon EF-S 10-22mm f/3.5-4.5... very reasonable lens used especially considering how awesome it is.
Or actually, buy the lens first for the best price/condition ratio you can find, then use the extra to buy the best possible rebel body (in order of ascending cost: Xt -> Xti -> Xsi -> T1i -> T2i ->). Remember, a nicer quality lens is better than a nicer camera body.
That lens is perfect for real estate photography, doesn't have a lot of distortion for that wide, and the colors look pretty good straight out of camera (I'm assuming you're not going to be doing a ton of editing since you aren't an experienced photographer.
As an alternative, you could go with lenses like the Sigma 10-20mm f/4.5-5.6, which sells new for less than 500 and is also excellent. The f/3.5 version isn't as sharp but the light advantage might be good indoors.
You could also go with a lower level Nikon body, and either of those sigma lenses, or if you stretch a little maybe the Nikkor 10-24mm f/3.5-4.5 (not quite as good as that canon lens but also very solid)
Edit: I hope the above posts didn't scare of the OP, not very helpful. Sure he's not going to be an awesome photographer but this is a get-the-job-done situation, not an artistic creativity situation. Give him a break.