The prices page can be found on this link: http://appshed.com/apps/prices Here you will see that Starter Accounts are free, and many teachers simply get their students to sign up and create a free Starter Account.
Pro Accounts are for businesses (single users). The cost will rise quite quickly if you are using it with your students so this won’t be the best option.
The EDU Accounts are a subscription-based service. We provide you with at least 100 logins with extended storage space. You also get access to many teaching tools. The full details can be found here: http://appshed.com/teach/appshed-academy