Is $21,000 to add a 20 kWh Anker whole home battery backup system a fair price?

I live in Florida and currently have a 48 panel 19kw solar system with no battery backup. I'm seriously contemplating adding a powerwall, but received this quote for an Anker system. I'm mainly looking for an emergency backup solution because I work from home and experienced power outages for days after Hurricane Milton last October, and also a similar outage a year or two before. It's frustrating having a decent size solar panel array that is useless when the grid is down.