You could always do what Valve did with their community made TF2 items that they made official. Basically whenever someone buys the item in the cash shop Valve cuts the person a check for their percentage, and no I don't know the percentage that would be between you and the modder.
Essentially you could take the mod on, make it DLC for the game and then cut a check to the modder every month or so for their share of the profit. Though I would suggest this ONLY for particularly good and lengthy custom scenarios, anything less isn't really worth paying for at least in my opinion.
Addendum: The kind of thing I am talking about being worth paying for is something on the scale of Nehrim. Nehrim is a massive total conversion mod for Oblivion that essentially makes it a whole new game with potentially dozens if not hundreds of hours of new, professional quality content with professional-tier voice work as well. If Bethesda had worked a deal with SureAI, the devs of Nehrim, and made it into DLC for Oblivion and charged like $15-$20 for it I wouldn't have minded that much. Though I do have to say this, the fact that something as impressive as Nehrim, and then the sequel of Nehrim being made for Skyrim called Enderal was made by modders for free with just donations is absolutely amazing. Kinda goes to show that passion is more important than greed.
Last edited by Raith; 28/06/14 04:30 AM.
