FAA flight test at £500...phew! Money for old rope.
Frankly with the prices listed on the previous web site, I'd jump on a £350 flight to LA and spend a week there, flying 6 hours per day to bang it out (flight test $400, no expenses, CFII $50 per hour, G1000 Approved Advanced sim $95 per hour).....My mate bought an ATC510 sim from Ebay for about $400 - all fully loggable time as it was an approved ATD. The ATC710 doesn't look much better.
The best thing you can do is find yourself a friendly FAA CFII in the UK, and pay him for the groundschool and endorsements, and as long as they fly with you for free, no laws are being broken. Then head to the USA to finish off.