You can either go onto the bracket of chess.com that has mentors, or just look them up in your area.
How do I find a good, helpful mentor?

It ain't easy. I went on the same search a while back. I tried a few different coaches listed here.
The problem is that the only prerequisite of being a chess coach is being a good chess player. All the coaches I tried lacked real teaching skills. The most important of which is understanding your students' needs and designing lessons for this.
You may have to do what I did: Determine on your own some of your strengths and weaknesses and guide the coach in addressing and expanding these.
I've been considering looking into finding a mentor. I need a good affordable mentor in the area, but how do I find one?