Bringing stuff back would be free.
I'm not talking about making trips just to bring back equipment in need of repair. I'm talking about bringing it back after other supplies have been sent up. The craft has to come back down, so why not put it to use both ways? Are we going to be throwing away equipment such as lunar drills, OMVs, or other high dollar equipment simply because it breaks, or are we going to bring them back to be fixed and reused?