The new SharePoint App store got three different Pricing models , when you submit or update you app you can change the pricing model at the last step of the submission , the available pricing models are

  • Free 
I think this model does not require any explanation you post your app for free no revenuee unless some hits to your website (if you are using a provider hosting app model)
  • One Time purchase 
The buyer will pay once and will use the application unlimited in this option you can set trail version support for number of days  and users 

  • Sold as subscription
The user can download and use the app, in perpetuity or until they cancel their subscription, for a recurring monthly fee.