Inexpensive CD Player

If the sound doesn't matter, in that price range you could get a pretty good DVD player from virtually any mass market supplier and use it as a CD player. I would check out Consumer Reports for long term reliability ratings. I have an Integra DVD now going for 10 years that is in that range. $500 would also buy a very fine Blu Ray.

a used Rega Planet or a Naim CD3 ... both are older models that just sound great! one or both may be in your price class

Time for a refurb Sony 595 from SonyStyle, often available for $60 shipped.

There's an Oppo BDP-80 for sale on Audiogon for only $225. This will allow your sister to enjoy every shiny disc format - BluRay, SACD, DVD-Audio, HDAD, CD, and HDCD. The high resoulution formats (BluRay, SACD, DVD-Audio, HDAD) can sound MUCH better than Redbook CD. Why not give her the advantage of being able to playback these formats?

-RW-

I'd go for newer rather than older. While you could pick up a better player if you go for something more than five years old, reliability would concern me. These current listings might fit the bill (I don't know any of the sellers):

Rotel RDV 1045 $250 (cd/dvd)
Marantz CD5003 $225
Cambridge Audio C340 $200
Marantz CD5004 $240
Marantz CD5003 $200

I don't know much about the Rotel, and it's a dvd player, but it's new and built like a tank. The Marantz players are very nice and also very well-built. I had a Cambridge and thought it was excellent for the money. If you want to go new, the NAD C515BEE is excellent for $299.

Best,
Andy