Im really not sure about US prices for poly-carbonate plates as Im from Israel but for a 1x1 meter with 5mm thickness it probably costs around 200 NIS here so around 50$. So getting 2 plates for 100$ or even less because of buying in bulk is very reasonable.
Again, im not from the US so im not sure how much will it cost there, just estimating
Of course there are some manufacturing costs for AndyMark and they should make some profit on a product they manufacture and distribute.
OK the sticker prices are a complete rip off. There is no reason it should cost more than 25$ each.
Teams that want to calibrate their color sensors to the same plate that will be in the field but dont have 140$ to spend on stickers are in a disadvantage compared to other teams that do have this kind of money
This is going a bit off topic but First is all about inspiring students to learn STEM fields. By putting a money barrier between students and the ability to participate fairly in FRC competition and learn about engineering and STEM you lose a lot of potential students who can learn a lot from this program. Just imagine how many more schools and students will join the First community and FRC if it would cost half as much as it costs now.