Was also a video[1] over on the Breaking Taps channel about casting clear epoxy resin to make your own lenses. Results were not perfect but good enough for some uses. Of course, that requires some actual lens elements to make the molds from, but it's something.
That's definitely an idea worth trying, though it was mentioned elsewhere on this post that you can 3D print and polish your masters for casting rather than relying on having the lens already.
[1]: https://www.youtube.com/watch?v=mfAGivG9Koc