It all depends on what your car needs. There doesn't seem to be any hard and fast rules as some items are mileage dependant and some age related.
So whilst you can get a basic quote for a C service, it can double by the time you include an air filter, combination filter, brake fluid, coolant change, gearbox oil and filters.... the list goes on.
Dealer prices can seem ok on a basic quote but I found that the difference for a brake fluid change between the dealer and an indie was over £100 so the differences overall soon rack up.
My quotes (for reference) for my C service 2 weeks ago (211 E270cdi 80k) was
Dealer 1 £525
Dealer 2 £632 (so worth ringing a few local dealers)
Indie £333 (came in at £327 when I went to pay)
That was inclusive of a brake fluid change and a new air filter.