not sure what the price is like put the kind of plastic sheets they use in vacuum formers comes in different thicknesses and different types of plastic, the thinner ones you can use scissors or knives. the thicker ones cut with a dremel, etc. to add mirror and color you can dye the plastic with synthetic fabric dyes and either 1-way mirror spray paint or use window tint. i dont think itll be cheaper than 25$ though.
Im still looking at ways to make my visor too.