Sammy
From some DASA stats I saw a while back the "Full Cost" of a GR9 per flying hour is in the region of £35k, whereas GR4 is less than £30k - the exact figures, I believe were 'Restricted-Commercial'. Typhoon was 3 times the amount at around £90k!!!
Don't forget "Full Costs" includes everything needed to support that flying hour (Med Centres, ATC, Fire Cover, Bird Scaring, etc...etc...)
I reckon that GR9 must be more expensive due to the cost of putting flaps of leather on all those flying boots!
LJ