I did a course that ran over five days, 2 hours a day. I did a course run by people in the official Butekyo association. This is the association and locations in the UK:
http://www.buteyko.info/fap_buteyko_...=UnitedKingdom
From what I can remember the cost was 100-200 pounds. You should be able to go along for an information sesssion for free which is also the first session. Just make sure you go to a professional practitioner, this method is amazing and it would be a lost opportunity if you didn't get anything out of it. I'll add that it requires a reasonable amount of dedication for at least 6 weeks to get any benefit.
Edit: Doctors a cautious of the method as it goes againts there way of treating people, that is with medication, so let your doctor know but don't let them steer you away.