After R&D you're just paying for the additional fuel to land safely. The control systems are already there for the other parts of the trip. Also, I assume it'

After R&D you're just paying for the additional fuel to land safely. The control systems are already there for the other parts of the trip. Also, I assume it's a lot easier to be sure that the rocket's in good shape if you don't have to check the interior for leaks, and whatever chemicals seeped in with the water?