videographer, I'm also new here, and looking into something similar. One thing you'll have to consider would be thermal expansion rates for different material. It's the reason people frequently 'float' the aluminum skin over the teardrop so that the adhesive between the wood and the metal doesn't oil-can the skin.
If you look at
this thread I recently started, I list some of the comparative material weights -- I've been looking at aluminum, foam, FRP and also Aluminum Composite Panels (which sandwiches polyethylene with aluminum).
There are also a lot of other options in the sign-supply industry, where weather resistance and light weight are often an issue. There's honeycomb-centered composites, polygal (a material you see in a lot of small signs like political ones in peoples lawns), PVC, and other materials (and mixes of materials).
There is nothing cheaper or lighter than foam and canvas, in what I've looked at so far. But there are other options out there.