Taking a cash option on a new car will net you virtually nil.
This is not true. There are still significant discounts to be had even for cash. Numerous brokers will happily put you in touch with dealers that will shave thousands of pounds off the list price regardless of whether you are paying cash or taking finance.
The dealers get kickbacks from finance contracts and get nothing extra from cash sales, apart from the standard commission.
It's true dealers get commission for selling finance products but of course its rubbish to say they get nothing but comission for cash sales, they still get the profit in the car, too, which is why many are happy to do a deal for cash. It probably wont be a lower price than you'd get for finance, so cash is no longer 'king' as it once was, but you can still get a deal.
My current car was (prior to haggling and discounts) £41,000.
And similar haggling and discounts would be available to the cash buyer.
How long would it take someone to save up £41k? Quite some time i'd wager - and by the time they'd saved that, inflation would have set in and that same vehicle (or it's predecessor) would be £50-60k(?), so hence still be unaffordable.
Generally if you've reached the stage in life whereby you are considering a cash purchase on a £40,000 car you've not needed to sit there for years 'saving up' for it specifically, let alone the amount of time it would take for inflation to take a £40k car to a £60k! Thats bonkers.
Almost nobody 'saves up' to pay cash for a car of that value. They pay cash for a car as that value becuase, well, they've got the cash already.
reject the vehicle in the cooling-off period, then offer to pay for full in cash, using the agreed price as their cash sum.
Yea, I'm sure dealer would LOVE you for that and would bend over backwards to do you a good deal in that circumstance.