If you look around turbo is 550£ atm
http://www.mk5golfgti.co.uk/forum/index.php/topic,28967.0.htmlS3 injectors is found on Ebay.de for app. 230£, not some right now though
Then you need the DV relocating kit, no idead of price in the UK for that but it won't bust your bank account.
You can drive with K04 and S3 injectors on your standard map, mine did 230BHP (it had also the APR 3" RSC TBE fitted), but the point is you can wait with remap and TBE until funds allows, aftermarket CAI is not neccesary at first, jut get a freeflowing filter and you are good to go.
All just IMO of course