I'm sure it would vary depending on location, cost of living in your area and the individual trainer's programs.
I am in California and currently have a new horse in training with a trainer I had used before to correct some problems with another horse. His monthly fee is $800. which includes feed. The trainer works with her 6 days per week and I receive a daily detailed report by e-mail on what was worked on, how she did and what the plan is for the following day. He is very professional and each horse has scheduled training times so I can go view the training as well.
It takes as long as it takes with each individual horse and I have paid less, but had inconsistant training.
Hopefully you can find a good trainer at a reasonable price in your area.
Best wishes for you.