BigT said:
Buy your own oil from Opie Oils for £60ish and ask the dealers for a price supplying your own oil and you'll get £100+ off those prices.
Castrol 10w60 for M engines is the one to use, and the only one Opie will recommend. You'll need 5.5 litres of it at about £13/litre in 1 litre bottles, £10/litre in 4 litre bottles, or £9.50/litre in 2x4 litre bottles - or you can buy just enough oil by buying the 'service pack' for £67. (all plus £6 postage of course)
OpieOils normally have discounts on throughout the year to give you another 10-25% off certain oils (plus your member discount) - current deal code (until 11th) is 'BMWSPEC' for any BMW spec oil for an extra 10% dicount.
I've had dealers falsely claim that it's 'against the rules' for them to stamp the service book if you supply your own oil, as the can't guarantee that it's not 'counterfeit'
If we can buy it retail for less than £9/litre, then I'm sure BMW can buy it for less than that in the quantities they're buying - if not, it helps you understand why they have to charge up to £180/hour for labour to recoup their losses

So the oil cost in an oil service should be 5.5L x £9 (£49.50) MAX, plus half an hour's labour at £140/hour (£70) = £120.
And don't forget that they probably don't use 5.5L anyway, as IIRC they don't empty it via the sump like a DIYer would, they'll simply suck what they can out through the dipstick tube with an oil siphon (to protect the environment from spills) and then top it back up.
We're paying upto £100 for the stamp - and that's fine with me, but I just wish they wouldn't be so machiavellian about it all by claiming the price is due to the price of oil (it's fully synthetic, it doesn't use a cracked hydrocarbon base, and it doesn't come from crude).