ClassiPress includes a function which allows you to create
subscription/membership packages, and if you make it a requirement on all categories that a membership package must be in place to post in them, then you could restrict posting to those people only. The default payment gateway included with ClassiPress is PayPal, however you can purchase
other payment gateway plugins from the AppThemes marketplace. Customers are emailed when their membership package is about to expire, and they need to manually complete the transaction to renew it (it is not automatically charged). You can choose in the ClassiPress admin dashboard whether or not you want those expiry emails to be sent out. Thanks.