just a remap will see the RS up to 300bhp

turbo , manifold , decat and it can bee up to 400 about £2500 worth

400bhp is the limit i think of the zetec in the RS , anymore than that and you will want to forge the bottem end (i know the pistons are already)

for a 400bhp zetec you are looking at jujst over 4k for the engine , then another £2.5k ontop of that to run the 400bhp the engines capable