As everyone has said, it varies greatly from area to area.
The biggest thing you should do is ask around.
Find out who has a good reputation, treats their horses well, and has lots of clients. If a trainer has a waiting list, I consider that a good thing because it means he has a lot of clients and referrals. Don't be afraid to dish out some money for a trainer who has been recommended by people you trust.
Whichever trainer you decide, make sure you have a full conversation about what you expect the trainer to do, and what the trainer expects he/she will do. You don't want the client expecting one thing and it doesn't happen because it wasn't discussed. So make sure you know approximately how long the colt will need to be there to fix the issue (granted, it can vary as training progresses so you've got to have wiggle room), how much ground work the trainer will do versus actual "rides", what he will be fed, where he will be turned out or kept, what vaccinations do they require, etc. You also want to find a trainer who is OPEN to you dropping by any time to have lessons with your horse. Sure, the trainer can train the horse, but they need to train the rider too.