I am trying to figure out how difficult or expensive it would be to add this feature

Question

I am trying to figure out how difficult/time consuming it would be to add the following feature:

We have a database with our subscribers and we want to send updates to paying subscribers. The catch is that we want these updates to be date dependent. Let me clarify.

Joe signed up in June last year. He has been receiving monthly newsletters since June. Now Fred signed up in April, cancelled in May and resubscribed in August. We want to send an update to Joe regarding his June newsletter. Fred was no longer a subscriber in June and we don't want him to receive the same update for various reasons.

Is this a feature that you would expect to cost 100's, 1000's, 10,000's dollars to implement?

**Edit: I should've been more clear, I was looking for a magnitude not an exact cost. It's evident, I know very little about programming which is why I came here. If someone asked me what it would cost abandon a well, I could easily give them an order of magnitude. I appreciate all of the responses; this is an incredible resource.