great question. First, keep in mind that salary is rarely discussed in an interview, and only if they bring it up first. Rather, the appropriate time is after you are offered the position. At that point, you will have leverage to negotiate, since it's the clear they want you. The best thing to remember is that their first offer, or the start of the range, is just that, a starting point. Some places have specific step levels, some have a set starting wage, some are vey open to negotiate. It's you job to understand the institutional parameters within which the hiring manager must work, and how much flexibility they have. Also remember money isn't everything and you might be able to negotiate vacation time, moving expenses, conference and continuing ed support, etc. Use this process as a litmus test for what it will be like to work with the people and policies of this library. How your new boss handles the hiring process provides a lot of insight about what it will be like to work with that person. Nothing is final until you get a signed offer letter, including a salary.

I just reread your message. Are you applying for a job in the same library system where you work now? If so, maybe you already know some of the policies and politics.