If he can get the reg/Vin he can stick it in here to get the quote and details from MB, otherwise contact his local independant who will give him the same at generally less cost. The B services are the more comprehensive with attention to brake parts etc https://www.mymercedesservice.co.uk/#/your-vehicle
Just to give you an idea of what to expect, my 2008 S204 needed a B3 service a year ago, local MB main dealer wanted well over £500, local indie specialist did the service "in accordance with MB electronic service schedule" using OEM parts and correct spec Petronas oil for just under £300.
At that age of car you could be looking at 4 year items (fuel and air filters) as well as 2 year item (brake fluid) as well as oil and filter change. Also if mileage is ~100k it could also be transmission ATF/filter change which would increaase the above prices by a couple of hundred (mine's due next January).
Another thing to check is correct thermostat operation (mine failed this year and has just been replaced, cost £150). Engine temperature should quite rapidly get to 80-90C and stay there, if it lurks around 60C it needs replacing.
Spark plugs as well every 4 years . As said above ATF service every 40k miles is advised , make sure whoever is doing the ATF understands that the Torque converter (which Holds half the oil for the gearbox) needs draining as well , a good Indy will charge about £200 for the "full" ATF change , some main dealers will try and charge £350 for a half ATF change .
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