PAYPAL
FYI: You don't actually need a PayPal account! PayPal provides a way to pay directly, with a Credit or Debit card, without the need to log into PayPal, or even have a PayPal account.
And, maybe later — especially if "modest" includes enough to fund a "self-published" edition — those [me included] who prefer a physical book they can curl up with, will get their wish.