Sure is a wide variety of prices indicated here.
When I bought my 2008 Malibu I took the car over to Nebraska where the Blue Ox company scheduled the install of baseplate. I did that and they also wired up the brake and tail lights, plus installed the switch to isolate a fuse so my battery would not run down. Total price out the door, was just barely under $1000
When I replaced the Malibu (it was developing transmission problems that GM wasn't seemingly able to find) with a 2007 Honda Odyssey, I decided to do the job myself.
I bought the baseplate from local RV dealership and that price was $420 and I hauled it home. Taking the front off the vehicle was a piece of cake, however the baseplate install proved slightly more difficult as the specs of either the Honda frame member, or the baseplate (one or other) was off by 1/8 inch. I had to use a chisel to make that slight indention to the Honda frame (and normally this isn't an issue). However I slipped and put a skin in my "condenser" ---- I applied the liquid soap to the skin, sure enough I created a bubbling leak. So - I went on e-bay and located an aftermarket supplier and had it shipped to me ($76 delivered to my house) --- cheap considering Honda wants a whole lot more.
So - I did the job for an end price of just under $500 start to finish, but wasn't satisfied there so I bought a custom rock protecting grill and put that in at the last minute too. Ok - price went up a little, but still under $600
I decided to not go the hard wire route - I bought magnetic wireless lights and they surely do work nicely. They cost me $390.
Now regardless of what vehicle I decide to tow my Wireless lights will be placed on that vehicle and good to go.
The job took me a number of hours, however spread out to well over a week because of the wait time for the condenser.
New condenser works great, by the way. I forget how much 134a I had to replace in it --- but wasn't a lot.