only need to use the student promotion for about 5 months, but there is only an annual plan.

There is only an annual plan, and you commit to pay for the year. Adobe do give a generous discount if you cancel your contract early, you only pay half the remaining fee for the year. 

there is a monthly plan with no commitment but it's over $70 per month. 

Hi

The specially priced Photography plan is annual plan is paid at 9.99 per month or can be pre-paid, and yes, there is a penalty for cancellation. You can purchase a monthly plan for 31.49 per month that can be cancelled. 

~ Jane