Unfortunately buying the performance parts is only a small part of the cost, you then have the costs you didn't originally realise.
For example you buy a ported head or get yours done for £450 but then you need to add a top end gasket set about £70, new headbolts £20, and new coolant etc.
You buy new cams for £400 then you need to buy some new gaskets £40 then you need new followers £5 to £10 each, or do you go for lightweight followers £250 and titanium caps £?
After each of these you would be wise to have a rolling road remap another £250 to £300.
Paul