Office chairs around 400 to 800$. It's god damn pricey but an absolute life change if you spend a ton of time at your computer. Are so much better for your back and butt and is worth the money 10x over considering the pain it'll save you.
If you can't fork up the cash, do a ton of research, learn a lot about specific models and then on Facebook marketplace (or any other local marketplace) search up "office chair". Oftentimes people sell premium office chairs without ever knowing, this way you can snag some for ridiculously cheap. Usually around 100-200$ but if you are lucky 10-30$.
Also avoid "gaming" chairs. Like most gaming related stuff, they're awful and you're just paying for the edgy look. I had multiple of these and each one was an ergonomic catastrophe, even expensive ones.