I think the HP photo smart scanner is within our price range, but I cannot recommend it: It grips negative strips or slides with rubber transport rollers, so you can be sure that you will have transport problems once the rubber surface show some wear. Furthermore, you cannot handle slides in glass frames with this scanner.
Some Canon film scanners are also supported by SANE, but you probably will not find a new one for <500 US$; the FS2710 is probably at 650-700 US$ at the moment. But perhaps you can find a good used one? Sincerely yours, Ulrich Deiters