I have a client who lectures, and wants to sell spots to his lecture online. I would preferably like to set him up with a solution that allows me to collect billing information on his site. My experience with e-commerce is in using solutions like Authorize.net, however this does not seem cost effective since I can't imagine he's making a huge profit off of this. I'm afraid he would lose money in the cost of using Authorize.net (or any payment gateway for the matter). I could use google checkout or paypal express, but this would require me to leave his site (although with google checkout, it looks like, from a glance, that I could just submit to their form from my server, and likely with paypal as well, but I don't know if this is against their TOS). What is the most cost-effective solution for accepting credit card payments in this situation?