We just bought a mini puphead ($65) for our Yorkie and it seems to work. It took a few days of training, but she finally went #1 on it this morning. The puphead does not have a removable tray, but for $65 vs $200....puphead wins. We only use it for #1 btw, never for poop.
http://pupgearcorporation.com/Produc...Mini-Dog-Potty
edit: we used a wiz-dog before too and it works ok. Except it STINKS when used with just newspaper. That plus the dog's feet will get pee on it since there is just a plastic grate and pee can sit on the top edges of the grate.