If you go the PVC route make sure you buy the UV stable version. The cheaper stuff degrades in sunlight until it becomes brittle and shatters into sharp shards. They make UV stable PVC products where this isn't a problem. PVC has a lot going for it as a building material if you're comfortable using that much plastic. Anchoring it to the ground is as simple as pounding a length of rebar into the soil and slipping the PVC over the top.
I can't go the PVC route here because the heat in summer can become intense enough to soften the plastics. What my family uses a lot are electrical conduits. They're easy to shape and are relatively strong and don't warp in the heat. I don't know if it gets that hot in WA.
Cattle panels are also as good as you'd hope. They're very popular for all sorts of purposes here, where they're readily available. I've seen similar constructions using cement mesh. I don't know how much support was hidden under the plants for this.
Also, don't underestimate the value of a few rods of rebar pounded into the ground. They can easily support nets and twine for the squash to grow on.
I have a weakness for using odd items as trellising. I've found nice instant trellises by wandering the neighborhood. The eight individual decorative panels that made the legs of a wind torn
canopy now make good trellises. I've got shelving displays from stores that were remodeling that break apart into flat black wire sections, also great trellises. I just pound a couple of pieces of rebar where I need a trellis and tie my flat metal piece to it. Usually these actually wind up looking very tasteful, despite costing only the price of a couple pieces of rebar. They're also easy to move around and reconfigure for the needs of different gardening seasons.
I do have some more tacky items, like a canopy bed frame and an old brass headboard that I picked up cheap at Goodwill. Those only get used in the back yard, but they work very well. It's not like the plants care and I don't mind some kitsch in the garden.
Edit: In looking for things to repurpose as trellises, anything metal can be hit with a coat of Rustoleum to greatly extend it's life. I wouldn't bother with rebar (particularly because pounding it into the ground increases the chances of it flaking into the soil) but anything kept above ground is fair game, for me. Oh, and did I mention rebar enough.