It got the old neurons firing though, and here is my design for a supper cheap, just as effective climbing machine. Of course, it hasn't been built yet ;-)
"notched pulleys"--these are pulleys notched for the rungs of the rope ladder. They keep the ladder from slipping and allow the "friction device" access to the edge of the pulley.
"friction device"--this is the fuzziest part of the design. It could be as simple as a screw that presses against one or both of the pulleys to control the climbing speed, or something more elaborate, of course.
Another item could be a set of counter-pulleys set to the floor to control swing. I would not necessarily want that because the built in tendency to swing causes you to use muscles and technique that would add to your fitness experience.
You could also fit a counter weight for the resistance control and/or to smooth out motion.
Has anyone built something like this? If not I am surprised.