Epson perfection 2450 or similar
These can be had for your price range, or the next model up which is a little newer. They do a very fine job with slides, bigger transparancies, and flat stuff.
Mr. Anderson: I have two of the nikon 4000's. They're OK. Maybe the best for the price but still have problems with corner sharpness and sometimes the digital ICE wrecks the image. When it works (97% of the time), ICE is a major time saver. Hate to say it, but it scans faster on our PC... 5,000 scans and speed really matters.
Oh, and cover it whenever you are not using it!!! un-cleanable dust will settle on the optics and cause hazy scans.
Cheers,
Andrew