On eBay I've found several inexpensive "secondary" screens for the Insignia NS-D7PDVD. This monitor is just awesom if you are looking for a small -but NOT too small, portable, TFT composite color monitor. The seven inch size just blows away anything smaller -you can actually see the content to be workable without squinting! The colors are great, the switchable screen aspect ratio, and especially the built in speakers ---AND THE PRICE, easily makes this your best choice for the cost range.
I'm using mine as the portable monitor for Raspberry Pi. I teach two Unix/Linux classes with it. I most highly recommend Raspberry Pi owners to give this monitor a real hard look... and then buy it!.
-Prof. Michael P. Harris
Del Mar College