There are many, many knock-offs.
The Russell Executive Mesh Chair is supposed to be nice, and like $230 bucks.
Anyway, here’s a weird Google trap for you, because I’m obsessed with link farms and bizarre fake pages like this:
In URL, first three words: aeron knock off
Then: generic text with that phrase inserted a couple times. Followed by a bunch of Google Ads.
Then: article of some kind, probably poached, maybe not, and a bunch of totally random unrelated news items…
You could probably auto-generate these pages, waiting for people like me to come by and (you hope) click on one of those ads and earn you $.05 or so.