Mine are all fitted and work well for around £20 an a hours work, well pleased with them.
130 fitted plus 10 quid for painting to colour of required, as for canbus... Whoever said that knows little about modern cars! What most people refer to as canbus relays (which is why he's probably thrown that into the mix) for towing are actually nothing to do with canbus at all, canbus is how ecus talk to each other via twisted pairs of cables with digital signals, rear lights just use 12v in 99% of cars, and the "canbus" relay is actually a switching system that takes very little current to switch towing electric lights on so bulb warning systems don't get all upset by funny loads on various circuits when a trailer is connected, hope this helps!
Just solder the reversing sensors into the reverse light circuit as they are designed to not upset the check bulb systems on modern cars
13 quid sound only Chinese sensors from eBay, work a treat
You can use reversing lights with built-in buzzer; two in one !