Looking for website developer for math education non-profit

Math inquiries Project (www.mathmirror.org) is a non-profit dedicated to the teaching and learning of math. We are currently looking for someone to help part-time in developing math practice exercises for the website. Given a simple math question, students need to enter their responses in the blank(s) and immediately move on to the next question if they get it correct. There should be a count-down timer as well, visualized as a shortening bar or something similar. These exercises will be provided for free on the site as a resource to parents, teachers, and students to sharpen their basic skills. We are willing to negotiate a stipend for your help. Thank you!