In all of our articles about taking online payments (for instance,
A Few Good Online Payment Multitaskers or our
Online Donation report ) we talk about the importance of estimating the size and volume of payments you expect in order to compare the costs of different vendors.
Andrew Page of
MAPLight did just that, and was kind enough to share his Excel model for calculating fees based on actual donations recieved. You'll likly need a bit of understanding of Excel and how Excel models typically work to use it, but it's a really nice framework that will help you think through the fees.
Download Andrew's Excel Online Payment Cost Calculator Thanks, Andrew!