There is no charge for re-mailing except the postage to the post office.
What you need to do is prepare all of your valentines or whatever else you want re-mailed for mailing. This includes placing them all in addressed envelopes and putting proper postage on them, just like you would do if you were going to mail them yourself. Put these envelopes into one large envelope. The larger envelope should be addressed to the postmaster.
For Romance, AR you should send your envelope to:
Postmaster Romance, AR
Romance, AR 72136
If you live in Arkansas, it doesn't take long to get the invites or cards back. You should give them about a up to a week. For out of state Romance seekers, it will take a bit longer.