CDs are polycarbonate and are sold for $20 for a spindle of 100. At a pretty good profit. "Bullet proof plastic" is just marketing buzzwords.
FWIIW, polycarbonate has to be quite thick to stop a bullet and is generally used in conjunction with glass. Looking at the chart[1], it is clear it will only stop relatively lower energy handgun bullets, not high power rifle bullets. For that, it requires a glass + plastic laminate.
[1] https://en.wikipedia.org/wiki/Bulletproof_glass
