I built a 130' free-standing zip line in our
yard for the kids to play on. I have used it to haul chunks of
trees now and then.
The "brake" is made from two wheelbarrow tires, which act as a shock absorber.
The cable itself is quite inexpensive. The fittings add up quickly though.
I highly recommend using a two-wheel pulley (I use a Petzl "Speed" pulley). A single pulley is much less smooth.
I wanted it to be removable, so the ends are attached to dead-man anchors (big rocks buried in the ground).
The only maintenance required is occasional turnbuckle tightening, and lubrication of the cable.
I can post some pictures or video if you'd like to see it.
Here's another aerial bicycle: