Ye I had a quick look, I've found a few cameras about the £100 mark waterproof and 50m cable, a TFT monitor or similar, a hard case, push it through with drain rods and it'd just be building / buying a skid and a replaceable lense. It should all be able to run off a 12v supply which should be easily wired up to a rechargeable 12v battery similar to the power packs you get for cars, to record should be able to wire either a dvd burner or cables to a pc via video out. I recon it could be done for around £200