teacherjoe: If you are trying to pay through Purchase Order than the minimum order is for three years. Otherwise, subscription is indeed yearly or monthly.
@FlorianF: It looks like you are thinking you can only order Take Home licenses which is untrue. In order to be able to order Take Home licenses you need first and foremost a On Site license on top of which you can order Take-Home Licenses. View the education FAQ.
@sletts: Are you sure you are writing in the correct topic ?
Those prices for C2 education have been set back in 2015, it's not a "sudden change" and a yearly subscription for a site-wide license is still the same price.
It sounds like you are talking about C3 pricing possibly. Although C3 system is far different from C2 so it may be confusing.
C3 is based on concurent seats you can assign/unassign.
You can read more on how it actually works in this page and this other one.
@TRMG: Uneducated and irrelevant answer.