pinhole cameras are on ebay for anything between 99p and ?40.
the wireless one attached to the front number plate of my Rover for S2N was wireless and could of been better, but then it only cost 99p. i would get a wire version for what you want to do.
if you buy a full colour sunvisor with lcd inside, that shouldnt cost you much more than 70-100 quid. again, buy off ebay from one of the Hong Kong dealers to keep the cost down.
Tin
PS nearly went to bump someone deliberatly on S2N - then i remembered the camera - sccrreeech.....