add in the cost of return flights to and from your intended venue, plus the costs of accomodation, food and local transport, plus travel insurance, hire car insurances and costs of visas etc
£300+$43/night (say for 3 weeks)+$20/day (food etc)+$0 (not always needed, many hotels provide transport)+$0 (don't need a car when you renting a plane)+£100 for visas. I make that to be:
£1100 or so. Now consider that in the states you can rent a VFR 152 for $58/ hr wet, instructor at $35 hour = $93 /hr. Say you need 30 hrs dual to finish off = $2790 (~£1500)
In the UK you will spend probably £110 / hr dual in a 152, £110x30 = £3300.
Total in the USA = £2600
Total in the UK = £3300 + landing fees + transport to and from, and not forgetting food for the duration of you training (I after all eat whether here or there
)
You seem to have given the UK a chance, now I would go to the US, finish off in 3 weeks, have a damn fine flying holiday, get experienced in US procedures in case you ever want to go back again (and flying in the US comes highly recommended from many on these forums), and come home with a nice shiny PPL ready for the summer season!
Cheers
EA