Get a rawr pipe as its called goes from airbox to throttle body. Improves induction noice. And if you have another car send the engine to be rece prepped. There's a company in pvw that do it. Bout 900 for a 1.8 and 1500 for a 1.9 bore aswell as the cams pistons and such.
There is no way you get anything 'race prepped' for £900.
It'll cost you more than that to mildly tweak the head!
Cams, installed properly with the right bits can cost you £900 alone.
There are no instant additions on a 16v...it's going to cost you.
170ish BHP for about £1000
190ish BHP another £2000 on top...
Break 200 BHP, another £2000+ again.