I built this homemade slider dolly modelled on the Dana Dolly for around £100 plus the cost of track.
It runs on 3/4 to 2" pipe, tube or rails, and would probably also work on angle iron.
Due to the 16 skateboard wheels its max wight is limited more by the size than any mechanical restrictions- I've rigged it out at as a ride on dolly by strapping a sheet of plywood on top and it carried me and a focus puller with no complaints.
I use it with 4' sections of 1 1/4" 10G alumnium pipe, or I also have a set of seamless connecting pipes for use with lighterweight packages.
I machined a moy/mitchell mount into the top of the carriage- I currently use it with a 75mm bowl adapter.
The end supports have junior pins for use on combo/ slider stands, but I mostly end up using it on a pair of appleboxes. I also tested a leg system made out of more pipe lengths.