This is where it's good to be a hoarder, lol.
I've Used one of the side rail panels of my old crib that I found in grandmas attic. You could prop it on an angle, or with 4 posts have it completely horizontal. You can pound some steaks into the ground. I've cut down pressure treated lumber, and Screw it on. I've also used galvanized 1/2" electrical conduit (left over from a home improvement project) as legs which lasts forever in the garden, you just have to have a hacksaw or better yet a sawz all to cut it to length. Then you can use a spade bit, step bit or Forster bit to create a seat in your trellis for the tubing to sit in.
