Hi Capt M,
I spent a tincey wincey bit over US$10,000 obtaining my FAA CPL/IR (Single Engine).
Add about US$3,000 to that for the ME Add-On to the Commercial with IR privilages.
So you'll be looking at £9000 based on around US$1.5 to the UK Pound, **without** taking into account spending money, transatlantic flights, Miami/Fort Myers/Orlando airport transfers (or hire car), accommodation etc.
However I had around 420 hours before I went to America to complete the courses together with most of the requirements such as the long cross country etc. The IR was Part 141, CPL was Part 61.
This was at a well respected school in Naples, Florida.
Best wishes,
Charlie Zulu.