Valve announces that the Steam Workshop now supports the ability to pay for mods and other Workshop content, starting with The Elder Scrolls V: Skyrim. Word is: "Workshop is now putting mod authors in business via a new streamlined process for listing, selling and managing their creations. Creators contributing to the Steam Workshop have the choice of listing their new creations for sale at a price of their choosing, or to continue to make their work available to players for free. Mods purchased from the Steam Workshop are available immediately for play." There are more details on this page, and here's a bit on their policies, including an approach to refunds that many would argue should also apply to full games:

Try any mod, Risk Free
It's still important to spend a little time learning about any product you are about to purchase. But, if after purchase you find that a mod is broken or doesn’t work as promised, you can easily get a refund of that mod within 24 hours of your purchase. View the full refund policy here.

Free, Paid, or Pay What You Want
With over 24,000 free mods available for Skyrim in the Steam Workshop, there will always be lots to do and explore for free. Now you can also find mods with a specified price, or mods where you can choose how much you wish to support the creators. The price is up to the mod creators.