PayPal doesn't cost significantly more than what a small online place can get from other payment processors. It's something like 3% + $0.50. That's also not much more than what a small business can usually get for in person credit cards.

This site does use buymeacoffee.com, which appears to be a dedicated payment platform. Its transaction fee is apparently 5%, which is steeper, but better for these small donations because of the lack of a fixed fee.