Given that the site will need to be able to calculate different fees (almost certainly), and that you probably won't want to configure a bunch of different Buy Now buttons, a better solution might be DPM. Short of that, AIM is even more straightforward, and given that SSL certificates are relatively cheap ($50 per year from Godaddy, for instance), it makes sense to pay a bit more for a certificate if it means saving even a few hours of development time. Don't limit yourself based on the cost of certificates or hosting, it's often pinching a few pennies while shooting yourself in the foot.
