ATS do deals through out the year on oil and filter changes for �20 could be less for a ford ka.(U will see them in the press)
Top oil is used no rubbish in fact the use the same oil when i get my merc serviced.
I have become very suspicious of getting certain garages, even well known ones, to do the oil and filter change. Twice I was told this had been done only to find out later the filter had not be changed. This may be understandable as to have in stock every filter for every make of car would require a very large stock. Just mark the filter casing beforehand if you are unsure.