Rolex Submariner Servicing

[achurch1]

Hello

New to this I have a bi metal rolex sub I sent it if for a service after seeing a advert for a special offer, the company is reputable but feel there advertising is a bit misleading they said a full service was under £400 including basic parts for a service which I thought was fine.
My query was the costs went up £90+ vat because its gold stainless bi metal and apparently requires more specialised cleaning, (what company stated when I asked why the quote was more ) the quote states gold stainless refurbishment £0 included.
total costs including parts is £900 Inc.

What do you think? Thanks