Did some research a while ago, I believe the Stripe nonprofit fee is unofficially 2.2% + $0.30 on the first 15k/yr, but they may negotiate with you to find some

Did some research a while ago, I believe the Stripe nonprofit fee is unofficially 2.2% + $0.30 on the first 15k/yr, but they may negotiate with you to find something in between that and standard. You do, of course, have to pay Interchange fees no matter what, there's no way to get to 0-fee with a card payment.