BIGGRED.CO.UK do all the brake repair/overhaul kits and is a very good person to deal with.
My kit cost me less than £30 to do both sides, but I had to have 2 new pistons at £9 each, one side had 3 jammed solid pistons the other side 2, so were not great, bloody shit to get out though the jammed ones two of which had to be ground out.
The pads will make the most difference, I use EBC REDSTUFF CERAMIC, and am very hard on the brakes, grooved or drilled discs make a massive improvement as well as they constantly deglaze the pads.
tabetha