Thanks for using Seesaw! We're committed to making sure the core Seesaw service is free for teachers, parents, and students. It is a key part of our mission to impact as many students as possible and having Seesaw available for free is one of the ways we do that.
We also offer Seesaw Plus and Seesaw for Schools, optional paid upgrades for teachers and schools who want to do even more with Seesaw. You can view a comparison of Seesaw, Seesaw Plus, and Seesaw for Schools features here: http://web.seesaw.me/pricing.