The price of batteries has declined by 97% in the last three decades:https://ourworldindata.org/battery-price-decline. And it continues to go down! The chart ends at 2018, $181/KWH. 2024 forecast is $94/KWH (half of 2018 price), 2030 forecast is $62/KWH. Thats just Lithium Ion. Newer chemistries are even cheaper. CATL first-generation cells (Sodium Ion) cost $77 per kWh, expected to drop to $40/KWH.[1]
Current estimate for a battery replacement is 4K - 20K. With energy storage's learning curve, this will be soon under $3K.