He wasn't haggling. He was mocking the blue check status symbol in King's face and audience.
$8 makes it cheaper than a Netflix subscription for something that previously exclusive and had no dollar value attached to it. It was literally unbuyable.
We're not really discussing reality if you believe that Stephen King gets status from the blue check rather than it working the other way around. There are people that do (sadly, pathetically) extract status from blue checkmarks, but they're only able to do that because people like Stephen King play ball with this system. The "blue checkmark status" could literally be phrased as "people as high-status as Stephen King and those like him".
Obviously, substitute Justin Bieber, Katy Perry, Rihanna, Selena Gomez, and LeBron in as appropriate to your particular interests.
The silly way Stephen King distances himself from the unwashed masses is the 400 million copies of his books that he's sold to them, and the various movies and TV properties built on his IP. Again: you're not talking about reality if you think people like King care about blue-check status more than Twitter cares about keeping them happy. You can wishcast that away any way you please, but that's all you're doing. Twitter needs Taylor Swift on the platform talking about Midnights. Twitter could kick Swift off the platform and do nothing at all to her popularity.
What's pretty clearly happening in these conversations is that Twitter-believers are conflating blue-check remora users who have no public profile outside of Twitter with actual celebrities. King is right, and Musk knows it: if he's smart, Musk will in fact find ways to kick things back to King, Swift, and LeBron to keep them happy. He needs them, and they don't need him at all.
$8 makes it cheaper than a Netflix subscription for something that previously exclusive and had no dollar value attached to it. It was literally unbuyable.