I'm not sure how many people work with Open Frames (a.k.a Scrim Jim Frames, Cine Frames, 4x4 Frames, etc.), but it's a handy bit of kit when you need to setup diffusion, a bounce, flag a light, or to hold a gel away from hot light(s). There's a million creative things you can do with these open frames, but many portable kits are going to run you hundreds of dollars.
Now obviously you're reading this because you don't want to spend a ton of money. So here's a simple idea you can use to build some simple frames (without tools) and can be found at your local hardware store. Just look for the aisle that carries Aluminum Window Screen or Aluminum Door Screen Kits.
You can get them in practically any size and some very large sizes. The channels are aluminum which can easily be cut down for custom sizes with a basic hacksaw. These kits are perfect as they use special 'corner adapters' that are designed to fit tightly into specially formed aluminum channels.
These ready made custom corner adapters make them ideal for use as a kit with quick assembly and disassembly of an open frame. I believe you can find 4x4 kits for under $15 bucks and not only do they work great, but they are super lightweight, and I think they look a bit more professional than pvc or wood. The flat tubing makes them easy to clamp to with little binder clips, C47s, etc.