Is $21,344 to install 18 Aptos 460 Black solar panels with a Tesla Inverter a fair price?

I am looking for solar quotes in Los Angeles, and these prices are gross before rebates. I plan to finance the system over 20 years. I am also considering adding a battery, with my main reason for solar being home backup for blackouts. However, adding a battery significantly increases the cost, so I'm trying to figure out where to cut expenses. I'm also trying to understand why the Enphase cost-to-output seems less appealing than a Powerwall, even though the overall Enphase system feels more robust.