I received one of the hundred buck ones as a birthday present a while back and installed it on our 2005 F150 Supercrew to see into that blind spot behind the tailgate. The camera is powered from the hot back up light line and getting a wire to that was the toughest part of the installation since it meant some garage creeper - mud in the face time.
When the initial installation was done I noticed there was an image on the receiver before the truck was on or in reverse. It was a neighbor's fifth wheel in his back yard two houses away! My other neighbor Jim (Across the back alley from the fifth wheel in the monitor.) had one of these things mounted on the back of his pick up cab and had just wired it to a toggle switch to help hitching his fifth wheel and had gone off and left the switch on.
Apart from that this system works just fine and makes hitching our travel trailer up an easy one person job. The receiver does occasionally pick up interference from cash registers, alarm systems, etc but those are minor nuisances.
A friend has a similar set up on his class C motor home but images on his monitor are fuzzy. The unit I have does give you the option of running a (manufacturer's extra cost option) coax cable from the transmitter to the receiver so that might help.