I'm still waiting on the camera so I can't give a full report but I bought a wifi transmitter (search on "wifi 903W" on amazon and you should find it) and a CCD camera for less than $80. I'm using an extra tracfone that we had for the screen but you could also use a tablet. I ordered the camera off ebay after verifying the transmitter worked (search for "white ccd backup camera" on ebay) and there were a couple of options in the $40 range. The best offer didn't seem to work and I went up until I was within 5 cents of the buy it now price.
I've tested it with another camera and it seems to work ok with the phone out in the driveway and the transmitter in the garage. Picture quality wasn't great but I think that was a product of the cheap camera I was using and it was about the same as the one I had on my old RV that was a dozen years old and cost a lot more. There is a little lag and it gets worse the further away you get but I don't expect it to be a problem for what I want the camera for and it won't be that far away with a truck camper.
Installation should just be mounting the camera and running 12 volts to it and the transmitter. Setup for the phone was easy. I ordered the camera off ebay (search for "white ccd backup camera" and there were a couple of options in the $40 range).
I figure if it doesn't work well enough I can still use the camera and either wire it direct (did that once and would like to avoid it) or get the non-wifi wireless setup like tadibrothers sells and not be out too much money. It will be a week or so before I get it installed and can give a full report but it is at least another option that saves you some money if you already have a phone or tablet you can use.