Turning on and off bronze

we are a non profit that will need bronze at certain times of the year can we pay monthly and go back to free when we are not using bronze.

Yes, you can upgrade and downgrade your account as it fits your need. 

How to Upgrade My Account

How to Cancel a Subscription and Downgrade Back to Free

I would also like to mention that we offer a 50% discount for non-profits. You can apply for a non-profit discount here - https://www.jotform.com/nonprofit/pricing/