Well I guess it depends on how snazzy you want it to look vs functional, and how much you want to spend. You could stack milk crates and run wire or boards across those?
You could use concrete block with timbers, our local hardware store did that with their green house. I have a neighbor up the road here that has a green house and plants only in the soil, says it stays warmer that way vs lifting the plants up. I kept a bunch of light weight pots on a heavy plastic folding banquet table one year just because that's what I had around to use.
