In California, charging at 40c/kWh during the day and discharging at 85c/kWh (for evening peak) would yield about $23 daily - or $8,400 annually.
Most Tesla's retain above 90% battery capacity after 100,000 miles [1]
Completely charging and discharging daily for one year is equivalent to 99,280 miles. A new Model 3 battery pack costs $15,800 [1] currently. 10% degradation is equivalent to $1,580.
Doing this currently would provide a ~7-year payback period on a Model 3.
[1] https://evannex.com/blogs/news/tesla-model-3-battery-degrada...
[2] https://www.slashgear.com/857917/replacing-the-battery-pack-...
I ask again - would you do that? Do you think your neighbors would do that? Do you think it's reasonable to base an entire power grid on that? What about if power starts to get cheaper on a particular day? Do you let the grid reach brownout status based on individual market pricing of individual actors?
Or do you just build some dedicated storage stations like any reasonably designed system?