You know it really depends on your area, and the trainer itself. A few years ago, I paid 950/month for 4 training rides and board. The trainer, was actually my old trainer. It was actually a very good deal considering she competes with her own home bred GP stadium horses and taught more advanced riders and horses.
I know some local western showing trainers, charge a little less than that for the same amount of training rides. I think it all has to do with how settled the trainer is with their own riding and showing and how much they've achieved. The more advanced the trainer, the more expensive it will be.