Question: 3rd Party X (Twitter) App

Hello! So, I had ChatGPT explain this to me, and I sort of understand what it's saying, but I was hoping someone on here could give me a better breakdown. X API has been opened back up for 3rd party companies to make an app, but at a cost - correct? How much is that cost per week / use / month exactly, and why are people not doing it? I really do not like the X macOS app, and the iOS app is just "a lot" for mobile. I use Twitter Control Panel for web browsing, but it’s just not the same as Tapbots Tweetbot app back in the day. Thanks in advance for your time and help!