A couple of things you should always do, ask for the bill to be explained and check what there saying is true, i.e speak to the tech and look at the parts that need replacing. i don't know whether you paid too much, although seems odd you paid more for your pads then discs and even paid £20 for them then i did for a set on a meg coupe from a main dealer!, its a case of what you see fit, i mean i only ever use a main dealer, the prices to other seem inflated but i am comfortable paying them as its ideal location for me, never ripped me off in the past with work that did not need doing- prime example was took the cup in as the brakes were squeaking, tech looked over, showed me the pads, discs told me about a notice issued by renault about the newer pads which fixed this problem, could have insisted on me having this done at £150 but said pads and discs were good- plus i could see that for myself, in all walked out of there without charge having wasted 20min of the techs time.