I assume you are from St Helena?
I would advise you and your sponsor to talk directly to the schools you have shortlisted. You may well find that you (or rather, your sponsor) can negotiate better terms than the advertised commercial prices. Remember that you will need to factor in accommodation and other living expenses for the 18 months or so that you will be under training.
You will also need to consider the selection procedures you may need to undergo for some of the courses on offer at OAT and Cabair. Have you undertaken any aptitude testing so far? What criteria did your government use to select you for training? Did they talk to the experts first? If you don't know, or you haven't been tested against established criteria, you may wish to consider carefully your next step. I would suggest, at the very least, you undergo a CAA Class 1 medical and the GAPAN aptitude tests. This will require you to travel to UK, I imagine, and will be an additional cost, but you can't leave too much to chance here.
Given your particular and unusual circumstances, it may be that CTC could in fact help you. I would strongly advise you - or, rather, your sponsor - to talk to all the potential schools and learn something about the requirements, the training, and the potential help available.
Scroggs