I think anything over $35 in its first year is a bit high. Sounds like a good idea, maybe start off with a profit margin of like $10 or something, and if it sells well in its first year and helps people, improve it for the next design and then use the testimonials to justify a price increase. If it gets to the 40+ mark its really just another text book for many people.
Alternatively, you charge only 10-15 but have it as a download for people instead and they print it off themselves or just use online - of course there are issues with file sharing then.
Overall 28-35 seems best.
Good luck and if you are going to make it, please do so before school starts so that it can be used throughout the year!