Outer Limits 4x4 Board

Does anyone know who makes a Sat Nav that you can plug a camera in to use as a rear vision camera?

I've seen one in a 4x4 mag @ $1,200 - any cheaper?

Doesn't need to be super fancy, as the camera is really only to line up a towball and a trailer.

What about a web-cam in a waterproof housing (like a torch) hooked up to a lap-top in the cabin?

Don't need a full GPS or anything - just a retail Sat Nav like Navman. It's for a mate who tows a heavy work trailer around job sites - he gets lost around town - ALOT!