I use a push pull hand control system on my car as I'm missing a leg. The hand controls add around £650 to the cost of every car. I used to make my own, to an almost identical design, for about £30. I didn't ever have much money.
Who can justify spending £650 on modifying a £500 car that probably would only last a year before being thrown away in favour of another car which has 12 months MoT on it? Usually the car I was disposing of was being got rid of due to an electronics failure that had eluded a cheap fix.
I think markets that have a captive audience get exploited. My wife put a 3 inch scratch in a neighbours bumper while parking a couple of years back. We went and told them, and they said as long as it was put right at a good bodyshop they didn't think we needed to go through insurance. I wish we had… The list of charges from the bodyshop included £5 for putting a disposable cover on the drivers seat, and £150 to go to Citroen to reset any error messages that "may" occur (not did occur) as a result of unplugging the parking sensors. That small scratch ended up costing us a few grand. But of course, the insurance companies would just pay it normally, so the prices keep rising…