If you go for a film scanner (not a flatbed scanned with a film scanning option), any scanner should be ok, as the cheapest one available can do 1800 dpi (check the next link):
But for possible image cropping and bigger prints more is recommended, of course.
1800dpi * 1½ inch wide slide/negative frame = 2700 pixels wide image on your puter. For a print at 300dpi it's enough for a photo 9 inches wide.
However, the scan quality and dynamics are quite poor on that scanner, so it's not just the resolution that matters.