I think £40 per hour is good value. I doubt you could get a decent car mechanic for that much. Once you take into account overheads, what's he earning ? £10-£15 PH ? not a lot really.
I really feel its important to pay a fair price for work you have done, other wise these fantastic small mechanics simply disappear.
I used to have a small marine mechanic near me in Ormskirk, I have been using it for years, my dad even bought a boat from there in the 70's ! But sometime over the winter it closed down