retrofitted backup camera installation for 2012 model
 

I'm looking to find the best way to install a retrofitted backup camera unit to my 2012 iTouring (pre-SkyActive) sedan.
I got a phone estimate of $550 for a license-plate mounted, rear-view mirror type installation, all-inclusive, from an aftermarket installer.
I see kits on the Internet from $80 up.
Does anyone have experience in purchasing and installing this kind of unit? How much should you expect to pay for a reliable camera and rear-view mirror installation? Would you recommend a particular kind of kit? Is it rocket science to DIY?
My Mazda is equipped with Bluetooth which I use for my phone. Is that a factor in choosing the kit or in installation?
Thanks -
Howard