Hi, I considered going this way at one stage so from what I gathered your route might look something like this:
PPL in UK: £6,000
100hrs ish hour building in USA (get IMC + night ratings at some point): £6000
ATPL theory (we'll say distance learning ie: Bristol): £3000
CPL in UK: £4000
FI rating UK: £6000
By my reckoning that is about £25,000 to get an FI rating limited to SE planes.
All prices are of course estimates and no doubt you could do it a bit cheaper or more expensive in various places. And don't forget to add on living expenses.
Good luck