Education Discount for Students/ Monthly (not Annual) Rate?

I am teaching a course in information design in the spring, and I would like for my students to use CC to create their class deliverables. The course length is approximately four months (mid-January to mid-May).

I'm trying to figure out the cost to my students if they purchase a subscription using their student discount, but opt to cancel early. I ask this because I want to be able to forewarn my students as to how the pricing may change should they cancel. I can only find an annual rate of $19.99/month. If they choose to cancel their student subscription after the course ends, what would the cost be? Is it charged at $79.49/mo (full price) for the four month period, do they have to maintain the annual subscription ($240/year), or is there something in between?

The university has CC available in select labs on campus, but I am considering adding CC to required course materials so that students can access financial aid funds to pay for a subscription (I also think it would be easier for learning if the programs were installed on their own computers).

Thanks in advance,

Andrea