I highly recommend Braintree. Variable monthly billing is very different from monthly billing from the card processor viewpoint. Most providers will let you s

I highly recommend Braintree. Variable monthly billing is very different from monthly billing from the card processor viewpoint. Most providers will let you schedule recurring payments, but only fixed ones. Braintree let you do variable billing, without needing to go through the PCI process, because the credit card information never touches your servers.