The Ketron SD is very popular here on the forum, but I think it is over $200. You might think about upping the budget, or look at a late model yamaha PSR keyboard to use as both an external soundcard and/or controller.

Roland and Yamaha make some starter keyboards that don't sound too bad for around the 200 mark. Or you could look for something used. Most used stuff is older and doesn't have the same quality of sounds as the new stuff.

http://keyboards-midi.musiciansfriend.com/product/Yamaha-PSRE413-61Key-Portable-Keyboard?sku=706168

A friend of mine has this one and it sounds pretty darned good for the money. Plus it is usb connect.

Good luch with the search.

Dang....This is addicting.

http://www.reverbnation.com/roberttrippmusic