Try the custom AI to help you find products that Reddit loves.
Fairly certain they mean this one, the FlexiSpot OC3B..
Personally, though, I always suggest checking craigslist and similar first. I use a legit aeron at work, which my boss got refurbed for $650 each. They are going on 10 years of use, with only 2 out of our 20 chairs showing any signs of wear and tear. (one actually needs repair, the lock on leaning back nolonger holds, the other the fabric of the seat has a hole, works fine still, just looks ugly)
At home I use (and greatly prefer) the Steelcase Leap, which I got used for $250. 5 years on it so far, besides my cat deciding to chew the arm rests, looks and feels new.
Both of the above chairs go for around $1000 new.
I've never found a sub $400 retail price chair that didn't fall apart within 3 years of purchase. But then these $1000 chairs last so long, and are fairly easy to repair (with plenty of replacement parts on the market precisely because they last so long, third parties can safely make the parts and know people will buy them) that buying a used one is a fairly safe purchase.
I used to go through $60-80 chairs every 6 months to a year and a half. $250 has lasted me 5 years, and reduced the waste I make and stress of watching chairs fall apart, getting rid of them, and finding new ones.
Flexispot oc3b on Amazon