Both Stripe and PayPal have a 2.9% +$0.30 credit card processing fee, per transaction. If you are a non-profit organization, it's possible you may get lower processing fees by contacting:
Stripe
Please email nonprofit@stripe.com with the following information to see if you qualify for a further discounted rate:
Your EIN, or a letter from the IRS designating your 501(c)(3) status
Confirmation of the primary email address associated with your Stripe account (if already created)
Confirmation that greater than 80% of your payment volume will be tax deductible donations.
PayPal
PayPal offers discounted transaction rates for confirmed 501(c)(3) charities for most products, with no setup, statement, withdrawal, or cancellation fees. Please contact Paypal directly for more information.