"Call for pricing" AKA prepare for a sales pitch before being bent over. I've seen 4 camera kits for as little as $130 (I'm sure there are more stealthy ones for a fraction more) on eBay, the question is how to incorporate them into the factory screen or an aftermarket unit like AVIN.
Look at this on eBay
http://www.ebay.com/itm/232589207471