(Disclaimer: yes, I bought a $180 4TB Crucial SSD too, but my family split the cost with me since they're going to use my Jellyfin server. Whether that counts towards the final cost is up to you. And the electricity cost is pretty negligible to run a Le Potato as a server, but I guess you can count that too.)
So this all started rather innocently. I was fed up with all the ads being shoved in my face with everything I do, so I finally decided that it was time to set up a Pi-hole on a single board computer. For me, it ended up being a Le Potato. I had never even touched Linux prior to this, so it took me a day or so to get everything set up. I love learning new things so I kind of got hooked on learning my way around Linux basics and decided that I was going to upgrade my setup to a Pi-hole + VPN using wireguard. That was kind of a beast to configure as a novice but I got that to work after about a week. Now I was getting ad free content anywhere I wanted on my phone. I rode that high for a few weeks until I realized that I was just scratching the surface of what I could do with my little $30 Linux server setup and this is where I really got to upgrade.
I had learned of Jellyfin from LTT and decided that I was going to test it out. I set up the Jellyfin server on the Le Potato and I was off to the races. Now I just needed content. I read through some of the wiki and settled on Mullvad+qbittorrent to find the content I wanted. With everything configured it still didn't really feel complete, so I set up profiles for my family members and gave them their own passwords to access the content. I quickly realized that 64 GB was not nearly enough (without a rolling library) and I was getting annoyed with having to constantly swith the flash drive I was using between the Le Potato and the laptop where I was downloading my content. So I went out and bought a 4TB USB SSD from Crucial and set up access as a NAS on Ubuntu with Samba.
It's just now finally set up. My family texts me to let me know what it is they're wanting to watch, I torrent it, upload it to my NAS, and Jellyfin streams that content to my family 100% free. I've turned my 6 family members into pirates and they barely even realize it.
Well, there's obviously going to be a lot of angles to that question but initial cost and the fact that large scale battery farms aren't necessarily needed right now stick out to me.
The grid as it is designed right now is capable of producing power at demand simply by spinning up more generators. There's no cost benefit (really) to generating extra power and dealing with logistics of storage while the extra power is not needed. Not at statewide scale and while the infrastructure isn't built already.
Let's for a second assume that a power company at statewide scale wasn't able to just spin up more generators to meet demand and there IS incentive to provide storage. The company looking at the market today has 2 choices. Buy batteries that provide a versatile/portable solution with no real local consequence OR spend money developing and engineering molten salt or pumped water storage.
Electrochemical batteries:
Gravity and thermal batteries: