There are lots of options like you probably have noticed. But two main options: Wired or Wireless. Wired is preferred if you have the time and setup to make it work as it provides a much better picture and reliabily. Wireless is of course a snap to install but can be tough to get working properly with all that distance to carry.
With wired you can either buy a whole setup with LCD, Camera, and hardware or if you have a GPS with a VIDEO input you can simply buy an aftermarket camera that connects to it like this.
For the total wired system I would have a look at the Review Safety Unit. Its highly rated and of great quality. If your looking for something less costly, I would look at the Pyle.
When you get into the wireless back up cameras it is hit or miss. The one from Peak gets decent reviews and I know a couple of people who use it and like it. I would recommend not going low cost on the wireless because you wont get anything worth keeping for any amount of time.
I'm looking for a good quality rear-view camera system for my RV, but I don't want to pay a ridiculous price. There are so many choices out there, but in your opinion what is the best RV backup camera for the price?