The war to sell you a mattress
The whole mattress industry is a scam. Actual manufacturing cost is $75-$300.  Mattresses are even cheaper on Alibaba.
Vacuum-packing memory foam shrinks mattresses for shipping, and now they can be imported easily.If you really want to annoy the US mattress industry, set up a review site and review sub-$100 mattresses off Alibaba.(Personally, I have an air bed which cost about $200.)