Gamemaker basic is free, interesting. And integrated with steam workshop.
Also, smart of valve to do this with the 3d coat: Your 3D models can be auto-compiled directly to the Team Fortress 2 Workshop from within 3D Coat! And the pro version: By purchasing this license you receive the rights to use 3D-Coat commercially.
In combination with valve saying somethig like you can do wtf ever with source filmmaker (if you don't make money off of valve's assets), you could use SFM and something like 3d coat to do commercial animated videos for cheap.