My older coach didn't have a camera, so I got a color, wireless one from these guys: https://www.tadibrothers.com/ It did a good job, but be sure and order the optional grid lines on the monitor. I didn't and ended up fabbing up my own.
My current coach has one of those big, clunky b&w ones that was installed when it was new back in '00, grid lines and all.
Believe it or not, I like the clunky b&w on the current coach better.
I was at Colaw Salvage in Carthage Mo(big, giant, RV salvage yard)and they had a whole shelving unit of monitors and cameras for the old systems. I didn't ask the price on the back up system, but, generally their prices are 50% of new on everything else I've bought.