Yeah I’d skip the chips away repair personally. Had one that was ok for some light bumper damage but another where I had a slight dent / scratch on a door and the repair was very average. You could see where it had been done after a few months.
We’ve got a local body shop that I’ve used a couple of times that have done a much better job. They’ll either do a blend on a part of a panel or do the whole panel from scratch depending on budget / damage etc. On a company car going back at end of lease they sorted out a few bits for me for a very reasonable cost and the lease car company couldn’t find any fault with the bodywork to charge me for. Used them again for a repair where lacquer had flaked off a bumper.
£250 seems pretty reasonable – but the £450 doesn’t surprise me either. You might find the cheaper one is doing a blend whereas the more expensive one is doing while panels.