If you are truly looking for the cheapest solution possible you will need to integrate payment gateway software to your site and contact a large merchant bank that you have an existing relationship with, like BofA – Wells Fargo – Wachovia – Chase Paymentech. Then you will need to find someone willing to haggle with you. You should be able to get something like $0.10 and 2.05% for qualified Visa/MC transactions. If you don’t want to integrate and locally maintain your own gateway, pay an additional $0.10 per transaction for a 3rd party hosted solution.