Personally I would get a normal Neo Geo cd than a Neo Geo cd Z for a few reason.
cheaper and easier to get
doesn't breakdown as easily
No games require patches unlike certian games on a CDZ. I have 95 games which is almost all of the Neo Geo cds and they all play fine
I guess since Neo Geo systems aren't that easy to find now I guess $100.00 is a good price for one. Also you might want to look to get a system with a bunch of games as you get a better deal for it that way.
Sorry to the best of my knowledge no system can play both carts and cds.