I bet that if you had been in the 'trade' the same parts over the
counter would have been discounted by 30 to 50 percent. Has the dealer
chosen to buy the parts from himself at the higher price and then passed
the cost on to you?

Many years ago, I foolishly put my car in for the 'free' 1000 mile
service. The labour was free and I was just expecting to pay for the oil
and filter. Both items came to around three times the price I would have
paid in the most expensive motoring shop. They itemised screen wash
sachets, the plastic bag put on the seat and the bit of paper put in the
foot-well. The price of these three items alone would have covered a
fair percentage of the cost of labour charges. The dealer went out of
business a short time later probably as a result of no repeat custom.