Can we pay for one month plan subscription ?

Can we pay for one month instead of the year to try it for our non-profit? 

Yes, you can select the Monthly subscription Term and since it is on Auto-renewal, you can downgrade anytime back to FREE to cancel the renewal subscription.

https://www.jotform.com/help/341-How-to-Cancel-a-Subscription-and-downgrade-back-to-free

Since you mentioned Non-profit, You can also apply for a Nonprofit discount. You can check this page for more information.
https://www.jotform.com/nonprofit/

Thank you.