Processed chemicals used for battery making cost many times the cost of raw materials, and it will be so until competition can weaken the big chem oligopolies currently dominating the market.
[0]its not. Batteries have exacting purity and qc requirements that meeting and maintaining is neither trivial nor cheap to do well even at small scale.
Silicon as a raw material is dirt cheap, too, but removing impurities so that it can be used makes it a lot more expensive.