Look at the tuning faq section - salvation lies within.
You don't need to brake the bank doing things the safe way, just as long as you read up and do most things yourself.
On the intercooler thingy.. the R intercooler is better designed than most of the after marked ones you can buy.. its just in the wrong place.
I would reccomend
uprated willwood brakes £450 totally essential,
Bump steer kit £120 sorts out understeer. you will need tracking done after
Clutch £ 330 plus fitting helix organic, fitting about £220 from olly or mike
Dawesdevice £40
Unichip £ 150 second hand plus a session on the rolling road to map it and set the dawes device, is better than fuel computer and more tunable to your car
Fuel pump £ 80 ish
Induction £ plenty of after market hks mushrooms about for £50 i'll sell u one
Exaust £300
you can fit the brakes, fuel pump, induction and exaust yourself, without much technical knowledge.
rolling road £70 per hour plus vat.
you will have 300bhp out of that lot no probs