Have you considered moving away from PayPal? They are a pretty hostile entity to deal with if there is any dispute about your money. Square is at 2.9% +$0.30 per transaction, which donors can probably just add to cover. Then you're reducing the amount given away to PayPal monthly.
Or, if you get your incarnate non-profit powers, this: https://donorbox.org/. Pricing: https://donorbox.org/pricing which could reduce even further.
Just some ideas. Maybe you've looked already. I'm certainly wiling to help in this, I have experience with both Square and Stripe. Square has a nice donation goal management feature which could be useful and less manual for the GMs. https://squareup.com/help/us/en/article/7184-set-up-donation-goals-with-square-checkout-links