Return has a 15 minute cooldown, allowing them to exchange things between Eorzea and Shirogane every 15 minutes. That's not so bad, is it? If they required more frequent visits the FC could probably given them some gil and activate 'Reduced Rates' actions.

They could also setup a free teleport location by activating the security token to their account as well. That way they can have a 0 gil cost way back.