Intrigued I looked into the cheaper "iPhone Android iPad WIFI car backup camera" some more...
3.4 star reviews from Amazon. Most complaints are about the 1 second lag in image displayed, or refusing to connect whatsoever. Most customers seem satisfied with theirs. You can check all the reviews in this amazon link
which sells this unit for $120 plus $10 shipping. If you decide to buy through Amazon, this is a better link
(only 3 reviews which is why I didn't link it for checking out the reveiws) to use since it's cheaper ($114) and offers free/Prime shipping for those with Prime.
I thought about buying it, but then I noticed that there are several other wireless rear view camera offerings on Amazon for considerably less and I got lost/overwhelmed trying to sort out which ones had legit reviews/might be better so I'm giving up for now.