There is a full build video on this project at: https://youtu.be/7vTOOd40AzI
It is built primarily using 3/4" plywood, bolts, 608 roller bearings, and EMT conduit. Since this sled uses imperial EMT conduit, the measurements are done in imperial and you will need to find 3/4" and 2" conduit for this build (which most home centers in the USA carry). The approximate price of the materials is around 100 dollars. The largest price is the 2" conduit which can often be found cheaper by looking around. Using 10' foot conduit you can flatten around 9' by 4'.
Conduit: ~$50
Bearings: ~$20
Plywood: ~$5
Bolts: ~$15
Optional Items: ~$10-$50
There is also a layout of a quick optional table if you don't already have a surface for supporting slabs that you would like to build this onto.