DSLR cage? (same seller and recommended) I bought one for 100$ in the late 2011. They don't seem to produce the same model I've bought though.
Then buy a simple shoulder pad and some handles and you're good to go.
edit: another seller is offering a very similar model of DSLR cage that the one I purchased last year.
Just in case you wouldn't be convinced, here's something that could do!
My current setup is actually the opposite side (cage on the left) so I'm operating the camera with the right hand (with an external monitor) :
Or make one yourself:
Made using 3/8 aluminium rods. Rock Solid and works well. Not as convenient when comes the time to mount it and un-mount it on the rails, but once it's on it, it's solid.
For the few times I'm using my adapter, I didn't wanted to invest a lot in a rail system, so I made one for a few bucks (under 50$).