Work for nothing ?
£500 for a 50 hour check is very reasonable there is about £80 just in oil, filter & gaskets. A bit more for maybe brake pads & air filter.
Other lubricants & cleaning compounds have to be paid for.
There is a eight hours work if you do the job properly plus the Dredded VAT at 20%.
That does not leave a lot to pay for the mechanic , hangar, heating, CAA approval fees, maintenance licence renewals etc.
That's only £10/flying hour for maintenance!, if the aircraft was on a 100 hour program I can't see the hourly rate being much different......... That is provided all the work is being done.