Transmit video wirelessly from on board camera over short distance
You don't state what "cheap" means to you, but I'm inferring that you mean "something in the tens of dollars".  I'd start with a used wireless video baby monitor, and modify to suit your specific design requirements.  

They typically include camera, IR illumination, modulator, transmitter, receiver, demodulator, and an LCD screen.  Lots of fun donor parts for a project on a budget.  You'll need to work out power supplies and getting composite video out of the demodulator, which will be specific to the particular model you obtain.