So - all done in the US. 30 days, 63 logged hours, and 87 flights in total.
I used Pacific Air Flight School at Long Beach airport who were great.
My cost breakdown was as follows (all in £)
Flights £553.23
Accommodation £1,174.85
Carhire & gas £271.46
Flying £4,484.73 64 hours £70.07
TOTAL £6,484.27 64 hours £101.32
So including flights/accom/car it was about 30% cheaper than the UK (assuming £140 for C172). Just on the flying it was half the price, and the experience was fantastic.
Hope these figures may be hopeful to someone.