Please send the money via a bank transfer, eCheck, or PayPal balance with PayPal, because then there are no processing fees and no limits.
We strongly discourage people from paying by credit card. Paypal takes a substantial fee, and there is a limit on how many credit card payments can be accepted.
On the "Review your payment and send" screen (which I got to by "Send Money," putting in your address & the amount, and choosing "Personal" and "Gift"), you should see "Payment Method" in the middle of the screen. You can change it there if necessary. "Instant Transfer from [your bank account]" is fine, as is "eCheck" or "PayPal balance."
It should default to Instant Transfer if you have a bank account with PayPal already.
Please forward a screenshot (or, if you get one, email notification) of your payment receipt to the seller when you have completed your donation so they'll know when to mail their item (or work on their deliverable).