Agree with all of these posts. My neighbor is a salesman at a RV dealer. He confirms it doesn’t make financial sense for most people to buy new, and you better be committed to using it even if you buy used. I’m sure he’d be happy to sell you one though :)
I’ve used a shock collar a few times and only had to shock the dog about the first 1 to 3 times they were doing the wrong behavior. After that, just having the collar on or me having the remote around my neck was enough for them to behave.