£120 at HiQ, going there, not even negotiating with my local dealership, they are always pricey..... once got a £780 quote on old M3, got it done for £280 at bmw specialist!
Whilst I agree the quote you had seems weirdly high (For context, I am quoted £280 base price for an oil service on my 530d, but there is 20% off at the moment which takes that down to about £230), you need to be a bit careful here.
Paying HiQ £120 to change the oil is not the same as having an 'Oil Service', which is a bit misleadingly named. It is little more than an oil service really but does include a couple of check elements as well as cabin filters and is a specified part of the BMW Service specification, whereas simply dropping the oil out and sticking some new stuff in isn't.
So, you may encounter warranty implications on a virtually new car if you pay HiQ to change the oil versus having an actual 'Oil Service' performed as per the manufactures specification.
I am unsure why you phoned them for a quote - use the BMW Service website linked to here for a proper menu price inclusive of the current 20% discount offer. It will be considerably less than 400 quid!
BMW do actually offer just an oil change - it is the same price as the HiQ quote you've received (Less actually with the 20% off).
once got a £780 quote on old M3, got it done for £280 at bmw specialist!
Did this £280 include the valve clearances, which if its an E46 presumably the £780 quote did?