I agree with Nick-B, get one off of eBay. I bought a Harbor Freight camera 11 years ago for our first MH, it did the job but did have a limited field of view and also had to rewire the monitor so it displayed reversed (it was a CRT type so it was fairly easy to do), too much of a pain now that you can get the systems off eBay for $40 or less. I had to extend the cable on the Harbor Freight one also.
When DW wanted a backup camera for her van this spring, I bought a camera for $13 and mirror/LCD for $20 from eBay, they work well.
Stewart, Brenda and kids
2008 Newmar Canyon Star 3410, now at a new home
2006 Roadtrek Versatile 210