Teacher Mentor - Voluntary or Paid Position

I would love to hear comments about whether the position of new teacher mentor is a paid or voluntary position at your school. In my district, mentors are only paid if they are an assigned mentor through a region's alternative certification program. I know that money can be a good motivator, but I am hoping to discover there are other ways of encouraging and gaining participation without incentive pay. I feel volunteering for a position like this really shows personal interest and a willingness to help a new teacher. Thanks!