I know there are a few members who are selling their versions for over $120. I personally, since this is more of an experiment for me, I am just going to go with a standard piece of aluminum from my local metal shop. I happen to have a friend who is a welder and he has a break that he can use to bend the bottom for me. I plan to drill the holes I would need to help attach items as I go along. After the movie, I might upgrade, but it is not super priority for me.
Others have tried thick acrylic sheets. To be honest, the plastic sheets are lighter, but more expensive depending on the variables (clear/color/thickness). The trade off is, you could bend the bottom on your own. While metal, though cheaper at a wholesaler, it would be best to find a break to make those clean bends. Just like the legacy packs, depending on your budget and the quality you want, that will determine the direction of your project. Hope this helps.