When hiring assistant coaches, you will see a salary range for each prospective assistant. Basically the high of that range is what the guy wants if he agrees to be a 1st assistant and the low of the range is what he is wants if he agrees to be a 3rd assistant and the amount he wants to be a 2nd assistant is somewhere in between. If you select each of the different Job Preference levels for a coach, you will see what that guy wants to earn for him to agree to be a coach at each of the three assistant levels.
When hiring, you should deselect the Job Preferences for all but the level you plan to offer to that coach. That will do two things: It will eliminate coaches who are unwilling to take that assistant level (they only willing to have a higher level job) and it will show the salary it will take to get the guy to accept a job at that level. While you can offer less, it's probably unlikely he will accept.