Hey Mate,
Actually I'm doing the FAA Dispatchers license. It is quite expensive the cheapest on-site course is Jeppesen which I remember was about 6000USD thats all course feee, books, exams, and most importantly Accomodation. I'm afraid I've not heard of any transition from an ICAO to FAA. According to FAA Regulations you have to attend the dispatchers course with a minimum time spent on it to be authorized to do it. I myself am actually doing a Distance learning course which is alot cheaper since you do everything at home. It costs about 2500USD but no free accomodation plus it takes over 2 months rather than the 6 weeks intense course. But I can't afford it. So there you go. Good luck.