In the past there has been an educational discount available on a monthly basis for other adobe software like Photoshop and Illustrator CC. If you go here:

 

Adobe Captivate Buying Guide

 

It would appear that there is no visible or readily available option for getting the educational discount for captivate on a monthly basis. You can try selecting the monthly subscription option, and on the next page see if there is a box to check off that says something about an educational discount. I apologize that I can’t verify this for you since I already have a sub to captivate, and can’t proceed to that page.

I also believe that the  education version is a flat rate for the current version. Once the version changes from the 2019 release to whatever it will be next, you will not get updated to that version without additional cost. Probably the same flat rate again, I would have to guess.

Beware: I am just a user, not from Adobe. But I have used an Education version before I retired from a university college. AFAIK the situation has not changed so far. That means if you are eligible for an Education version that you cannot have a subscription version, only a perpetual license at a reduced cost. With each full release you’ll need to buy a new license. Have a look at:

Adobe Captivate (2019 release) – For Education