I had to finish a lure, and test it, before I made this post.
First off, I am not a commercial lure builder. I make them for fun for me and my friends.
I put a bill in a jointed lure that wouldn't swim well, and it worked (see the gallery)
I didn't have any lexan or other bill material in the garage, but I did had hundreds of Plano dividers.
I cut out a profile of what I thought the bill should be, left it a little long, so I could trim it with a pair of sheet metal cutters at the test pond, and epoxied it in.
It isn't clear, but it's translucent, and it's flexible, so it wouldn't work for crashing lures into rocks, probably.
But it's rigid enough for wake bait lips, swim bait lips, and shallow cranks, which only have to deal with branches.
The material is tough, so I don't worry about it failing any time soon.
And it's not really noticeable in the water.
The best part is it's cheap, available, and it works!