Ouch we are expensive here in Denver. Rates are $1000 to $1500 a month for a quality race horse trainer and it can go higher if they are working with an Arabian as opposed to a quarter horse. I even heard of one trainer who got a $5000 signing bonus!
Rates varie from region to region. First make sure to conduct a survey of trainers available where you live. If there is a contract involved read all the fine print and even have a lawyer look it over. Watch out for the fine print because there are unscrupulous trainers around.
Here in Houston the rates are between $300 and $800 a month for a good race horse trainer. It really does depend on the age and breed of the horse that you want trained. I'm sure the prices are different depending on what city and state you live in.