You can find much cheaper batteries. But they will require additional components that are included in the Powerwall, will be less integrated, less pretty to look at, the mobile apps not as pretty, more complex to purchase, etc
Example 30kw for $8k. https://signaturesolar.com/eg4-ll-s-lithium-batteries-kit-30... or https://batteryhookup.com/products/new-24-56kwh-lifepo4-batt...