The one thing I have not seen anyone post is casting their own dice. Make a mold of the dice and then cast what you need. Unless you are selling them, I doubt that FFG will bother with you. Now, it will limit your options on material, but I think it is a viable idea. Now it may not be cheap to start, but I believe it could be cheaper than 3D printing. Also it should also be less sanding and polishing.
I have a friend that does resin casting and he has some clear resins which might look good. Should work fine for the d6 and d8 but I'm not sure how to make a good 2-sided mold for the d12. Might give it a try though.