Just got mine done at Batemans for an oil, brake fluid and MOT cost £323
I would get it done at a BMW garage for your service history not an indy, especially when the cost shouldn't be miles apart. Potential buyers dont like non BMW service history on an M. When it gets to a high milage fair enough but its not so go BMW
Also to add try and get it done at an BMW ///M dealer, bot all are M specialists. My experience between my local Lloyds who isnt and Batemans who is like night and day. They did a mini inspection of the car and gave it to me as reference and is good to put in history for potential buyers. They also printed off the full history of the car to check it off to make sure it was all done correctly. Was a fantastic service and talked me all through it, best BMW experience ive had anyway.
Car feels incredible, feels like its gained some horses from somewhere.