I think your best bet will still be second-hand. I was actually thrifting last week or so and there were 2 floppy boxes (empty, room for approximately 10 3.5in disks) but I didn't get them...perhaps I should have.

Make sure to add a couple silica packs or some other dessicant to the container.

like these?

try old computer shops, that's what I did 😀