I was looking at some of the life raft accessories and I came across some inflatable solar stills. I realize these are a very slow way to make water ready to drink, but I thought they might be useful and they fold down pretty compact when deflated.

Whenever I see sources for them we're talking ~$200 or more! They have a simple design and look like they cost almost nothing to produce... Is there a reason they are so expensive, and is there a cheaper alternative out there?