I was lucky enough to be able to pick up a micromark b/w 5in tv/monitor and b/w camera from a store in cardiff called "The Range" not sure if it is a chain or not. It can only take one camera which wasn't a problem for me. It is all set up to run on 12v and has a single lead from the camera to the monitor which feeds power to the cam and a/v signal back to the monitor.
A similar item is http://www.mismo.co.uk/product/247eMM23072.html
but this has ability to take two cameras and is more expensive (I paid £50).
If anyone is interested I will find out the model number tonight and you may be able to track one down.