Buy it on: Amazon
Amazon Basics Executive Chair may not specifically be a gaming chair, but it's exceptionally well built for its price point -- and will give you more reliability some of the cheaper PC gaming chairs out there. It's really comfortable to sit in for long hours and has a sturdy armrest -- one of our editors has had one for nearly a decade and still uses it comfortably every day.
Its adjustability is limited to height and tilt like many other chairs at this price point, and it doesn't have the ergonomics of a proper PC gaming chair, but your back certainly won't be complaining.
If comfort is your biggest priority around the $100 price point, this is the chair you want.