For those with a small amount of skill and a few tools, this is a nice project for these winter nights.
https://www.zombiehunters.org/forum/viewtopic.php?f=14&t=86433&sid=55def0c7d00d7cb948d6cb26308b4929There are very good pictures and specific instructions on what shapes fail and which worked better.
NOTE the paint to cover the white PVC.
The author used 1/2 inch diameter PVC, and I would try 3/4 inch dia. for added strength with very little extra weight.
PVC pipe comes in different wall thicknesses and the thicker wall is stronger.
I don't know how long this pack will last under heavy use, but a little care in how you handle it will go a long way to extending the lifetime.
One problem I see is that replacing broken pieces will not be a simple job and you would need to have access to spare PVC, saw and PVC glue. It is possible to make "splints" with other PVC pieces (or just wood sticks) to support a broken piece.
Certainly lower cost than buying an Alice frame in the military surplus stores.
I note the suggestion in the comments below the original post, that using plastic Electrical Conduit will make a frame with higher temperature resistance. This could make a difference if, for instance, you leave your frame near the camp fire and it melts or deforms.