Authorize.net is a payment gateway. I don't believe they act as a merchant processor. You need to have a merchant account for that. cdgcommerce.com would do that, but there are many others. They are just one I've worked with. All you need from your credit union is a business checking account.
Basically what happens is a credit card (or eCheck) is sent to Authorize.net who verifies it and tells the merchant processor (cdgcommerce) to deposit the funds from their account into your checking account. There's more to it, but that's basically how it works.
www [.] cdgcommerce.com/internet-services.php talks about the fees. Someone at cdgcommerce will be happy to explain in detail. They were very easy to work with and understand it better then me. It does take a couple of days to get setup, but it's the most cost effective way to accept credit card payments.
I should really get a commission for this
