You really need to look at the screen resolution when you buy, because the screen size doesn't match the resolution at all. I've seen 10" digital frames with 640x480 resolution and 7" ones with 800x600. The really crappy ones are widescreen with about 500x320, but those come as big as 8" or so. I think they look terrible.
I've attempted to buy 2 of these online during sales, and both times they've been damaged beyond usability when they arrived. I got a 10" that was 1024x768 for about $170 (cracked glass) and an 8" one at 800x600 that was simply destroyed when it arrived, that should have cost $150.
My personal specs are 8" or larger in a 4:3 format (not widescreen), 800x600 minimum resolution, uses SD cards, and has some sort of ability to play avi or mpeg files. Remotes are sort of cool but sometimes the screen can't be set up or programmed if you lose the remote, so read the reviews.
$160 or so ought to get you a good no-name one, but quality will be hit or miss. If you go for a kodak or other name brand one, expect to spend over $250 for a halfway decent one.