hi there,
i looked into this recently, and initial training is 5 day course about £500, but that only qualifies as a level 1, you then need x number of hours and another course to progress.
we recently looked at using abseilers on a job, but in the end have gone back to the cherrypicker option.
however if you do decide to do it, and have all the relevant insurance etc, then let me know as i may have work from time to time.
regards
martin