Plastic pipe works beautifully;
just stick a piece of re-bar (iron "sticks" that are used to hold concrete in place) about 16" long in the ground with about 8" showing above & put one end of the plastic pipe over it;
place another piece of re-bar opposite the first piece so that the distance between them is the desired width of the support, & bend the plastic pipe & put it over the 2nd piece.

Do a row of these, & put your row cover over them & secure it at the base.

Electrical conduit is also inexpensive, but you do need to buy the special tool to bend it.

The bending tool isn't terribly expensive so it would be worth it if you are making a long tunnel.

At one time a plastic "tube" of poly was available, and you set that on the ground, put your plants inside, and kept it inflated with a small fan, sort of like a bouncy castle. It made a frame-less greenhouse.

{{gwi:52022}}

I can't see how that plastic would hold up to the winter winds, possible fallen snow but obviously it worked for you as your plants are well established.

guavalane - how do you keep the cover from flying away? how much trouble is it to lift the cover everytime you need to pick the produce or apply fertilizer or anything else to do with the soil/plants ?