Depends on what size monitor your looking to add. I have Blaupunkt 7in I got at Fry's Electronics for ~$200-250 but a friend of mine found a off brand one online for only 100 bucks for a 7in.
12710 Executive Drive
That's a location that's listed in your area. Fry's should have everything you'll need to do the project and some you havn't even thought of. Have fun, sounds like a good idea.