Here are two good examples of successful SaaS apps that use both tiered pricing and pay-as-you-go: 1. Mailchimp - http://mailchimp.com/pricing/ http://mailchim

Here are two good examples of successful SaaS apps that use both tiered pricing and pay-as-you-go: 1. Mailchimp - http://mailchimp.com/pricing/ http://mailchimp.com/pricing/ 2. Campaign Monitor - http://www.campaignmonitor.com/pricing/ http://www.campaignmonitor.com/pricing/ I'm guessing that they do this to serve both markets: developers and B2B customers.