When a merchant is receiving funds via PayPal, those funds are deposited in his PayPal account. You can maintain that entire balance in your PayPal account and reuse it, or you can withdraw and settle those funds out to your bank account. This can be done on a daily basis. It's called an auto sweep functionality. We do not charge merchants for the ability to withdraw their money into a bank account, and they can do that on a regular basis. It comes in as a deposit that their bank, as far as I know, should not be charging for.
I've never heard of any fees from banks for accepting donations from PayPal. I've never heard of that, but I'd be happy to get a formal answer for you afterwards. I can investigate it for you.