Membership packs can be created in ClassiPress, and these are all based on an unlimited amount of ads for $x.xx for xx days setup, which appears to be what you're describing. You can see the package settings here on the
ClassiPress admin demo. Note: not having a membership doesn't restrict others from viewing ads, but of course listing ads themselves is restricted to only registered users who sign up for the package as per your settings.
There is already a function built into the theme which will email a user when their membership pack has expired, allowing the option to renew. Thanks.