Ring up another dealer and ask them or the price of a filter - usually £7 - £10, then oil, usually £40 for 4 litres shell Advance, then phone them up and complain.
Get an explanation of their racketeering, mention that UKMOC are curious as to how they justify these ridiculous prices.
Personally I reckon the blokes made a mistake.
Did he have a shaved head?
Crust