Where do i begin for a service business site?

I have developing we applications for many years. I use asp.net and many others. .Net is my perferred choice.  I know how to create an E-Commerce site selling products using the .net techonologies and a product catalog and shopping cart.  They have many free packages out there.  they have mojoportal, nopCommerce, magelia and others. I know how to set this up and brand them.  My question is what bout a site that Sells " a service" such as, people pay to log in and use the services you sell on a site. For example, how do i sell a to someone the ability to use my site as a CMS system. They pay for their montlhy subscription which expires at a certain date. DO they have starter kits out there for this? Or do i have to custom develop this so that when a payment is processed it sets an expiration date ofr their user credentials in thier profile unless their renew hte date is reset? I havent found any starter kits on this unless im overlooking the simp ...