stage 3 is around £500 and can buy kit from woodford, e.g. green injectors , 3 bar map sensor ,stage 3 chip.

you will need rs500 intercooler and a higher spec turbo ( t34 ) aswell and if a standard head gasket that wont last long at that spec.
Then set up price aswell prob around £150-£200.

After this stage it gets more costly