thats a veeeeeeeery difficult question to ask because it all depends on the salary of the staff member.
obviously the better the staff member the higher the salary will be, but if you find a trainer who has a pretty low salary for his skills then he will be expensive.
I suggest you look and watch the staff sales and see what trainer type you want goes for, based on that you can see how much you could expect to pay. Obviously people want the lowest salary as that way they save money over time