After removing the workshop file restriction size around a month ago, Valve and Bethesda have released yet another change to the Steam Workshop. Starting today (alongside Skyrim's free weekend and sale), Steam users can now sell their mods in the Workshop. This works similarly to a DLC or micro-transaction system.
Users who purchase mods can refund them within a 24-hour period of acquiring them. Prices currently range as low as $0.30 to as high as $7.49 by default. The "Pay-to-Mod" system uses a "Pay what you want" method of purchase. Users can pay set amounts of money for the mods. It should be noted that free mods will still be available, and mods from third-party sites can still be used on the Steam version of The Elder Scrolls V: Skyrim. Modders can still upload free mods without the need of verification by Valve, but attempting to upload a paid mod to the Steam workshop will still need to be verified by Valve. The Debut Pack of the first of these paid mods can be purchased as a bundle, and is currently on sale.
More info can be found on the Bethesda and Steam blog posts.