Re: Materials are available for cheap
Rebar is solid. A tube is stronger than a bar with the same cross-sectional area (because the material is distributed further from the center). Actually, a much lighter tube is stronger.
But as a piece of art, a rebar-bike OK.
Now, on the theme of the thread, yes, the whole skill of M-bikeing is making the machine cheaply. With a large budget, it's easy to make a m-bike. The skill is finding parts that are easily and cheaply available. Finding something usable that was mass produced for another purpose is the usual trick.