I recently saw a concrete parking lot being made. This was after hours,
so no one was around to ask. They had the forms made, and had rebar
placed about every 2 feet in both directions. Under the rebar they had
small plastic "stands" to keep it off the ground.

What are these things called, and where does someone buy them? Also,
what did they use before they made these plastic things? I plan to pour
a pad of concrete in front of my garage soon, and think rebar should be
used, but I was just going to use rocks under the rebar. Actually the
thought was to buy some of those cheap patio blocks, which are about 1.5
inches thick and bust them up into pieces for this. That way the rebar
would all be about the same space off the ground, and those patio blocks
are pretty low cost. Possibly cheaper than those plastic things.

On the other hand, I was wondering if using that metal mesh material
which is sold in rolls would work just as well as rebar and which would
be cheaper to buy.

Any concrete experts out here?