TheOptimizationIdiot - 1:11 am on May 1, 2013 (gmt 0)
Once you've got the requirement for active ongoing maintenance, a one-time inclusion fee simply makes no sense as a business model. Who does this?
Search for [paid directory list] in Bing and click on result number 3. You'll find a list of plenty with the pricing, length of agreement (including permanent), etc. on the landing page.