Sounds like you have a sharp trainer!
I think you will have to weigh your financial issues, and whats important to you. You would know best what you can afford and do!
As for the trainer, very sound minded to wait if the horse hasnt matured. There are so many 30 and 45 day contracts floating around, that what happens afterwards? Is the horse sound to start riding? Sure you can have them broke in a week, but just as fast as you jump on, can be just as fast as you fall off! Any I work with, its until the horse is capable and sound, and even more after. You can't really put a solid time on one and call it good. They each learn and grow at their own abilities!
If you have the time to invest in the ground work yourself, thats the question in my opinion! Because if not, maybe best to leave as is!
Dixon's Red Hot Ember