If you were up in the northeast my mate does a diesel for £110 so with a belt as well £250 would be the max i think and thats with you service book stamped.
Not fussed about stamp but i'd like to see the belt changed and i might as well get everything else changed whilst it's in there. I just thought £485 was a bit steep, still i suppose with fuel it might be cheaper to come and see your mate lol.