£500 thats cheap. I'm 36 with 15 yrs of NVB and mines a TDCI at i pay about the same as you and mines nowhere near as modified as yours. I suppose it may be to do with where you live to but t £500 thats very good. Hope you make your money back. Try posting the bits on the Focus ST Owners forum and put them on here too. Good Luck
I pay less than that on my tdci, im 24 with 4 years no claims!