Another thing i might add...is think long and hard on where you do the IMC rating.
For instance in the US there are not many NBD approaches or NDB's, where as in the UK there are tons of them. Plus you will have to get an M1 VISA. By the time you have the M1 and paid your flight to the US then you have already spent more than it would cost to do at home.
I would only consider doing it in the states if you plan on doing a big block of hours or MEP or something that would justify spending more money on doing a cheaper course.