As most of you know, chassis for projects can be quite expensive.
If you need a cheap chassis for a project or experiment try your local charity shop for baking pans. They do come in various thicknesses of aluminum. (If you are really lucky, you might even find some old steel baking or bread pans.
Want to bend your own? Used aluminum cookie sheets can be cut and bent. Try for the ones without the non-stick coating. (It can be hard to solder to Teflon & the like.
Shielding: Old COPPER window or door screens, and also the screen door protectors, (which can also be bent into chassis).
I even saw an article where the chap built a project on 1/4" mesh screening. Just cut, bent & folded it to make a chassis.
A couple of old aluminum baking/ bread pans can be hinged together to make a shielded box for a project too.