here is some random camera with 1.8W consumption.
MobileVideo4Less.com: NEW! Flush Mount InfraRed Night Vision Color 1/4" CCD Keyhole Camera
So, a total system cost of about 10W and about 5 pounds of wiring, mounting, equipment.
So how much power is used by a pair of mirrors at 100km/h? (someone with more FE experience can field that Q)