You can either:
a) Convert to a Zetec/Duratech/Fireblade - but this will cost a minimum of £3K, probably more.
b) Get someone else to do something - expensive.
c) Do it yourself, in which case it is mostly parts costs.
d) Get a 2nd hand one (ebay) - very risky but bargains to be had.
My 2 pence worth is basically you need to sort the exhaust and port the head. Then you need to look at a differnt cam, with vernier duplex gear to run it properly. This will usually mean upgrading the bottom end. 3d Ignitionis a great upgrade, but expense. There is loads of stuff in the archive about specs, and even costs of different bits.
Depends on what you want in the end.