You can do that in software, along with stitching panoramas.
Google exposure stacking software and panorama stitching software.
A program called Image Stacker can be had for less than $20 and can do wonderful things.
I would also recommend becoming familiar with Gimp, the free Photoshop clone.
For your price range, just stay with one name-brands and you'll do fine. Today's $100 cameras will give you roughly the same electronic performance of cameras costing 10 times that much 5 or six years ago, the only difference is, in all probability, the older cameras had better glass.
If you really want to maximize your money, buy used from a reputable dealer, just don't go too far back as your performance at high ISO will probably suffer.