Amongst the mass of junk chairs on Amazon there are some under $300 choices that are considered bearable, notably the Mellet (sold under various brands including here and here) and the Ticova Ergonomic Chair here. At worst if you don't like one you can take them apart and ship them back to Amazon for a refund.

You can certainly get usable chairs for under $300 on Amazon - the Clatina Mellet (Costway version here) or the Ticova Ergonomic chair here for examples - but these would not in any way be an upgrade from an Amia that is in good working condition. Quality office chairs have gotten very expensive in the last few years.

$300 can get you something used but it can be hard to find something you like in good condition. Old Herman Miller Aerons of a similar age to your Amia can sometimes be found in your price range for example.

Ticova Ergonomic

https://www.amazon.com/Ticova-Ergonomic-Office-Chair-Adjustable/dp/B0B9YG2LJN

There should be a checkbox to apply a $50 coupon for a $140 final price tag.

Either of the chairs below will likely be better for you. People generally complain about the Hyken’s mesh seat sagging soon after purchase.

https://www.amazon.com/Ticova-Ergonomic-Office-Chair-Adjustable/dp/B0B9YG2LJN be sure to apply the $80 coupon just below the price listing

https://www.amazon.com/COSTWAY-Ergonomic-Armrests-Adjustable-Breathable/dp/B0B17ZRT6N this one is just over your budget, but it comes highly recommended as best in class in this price range by numerous sources

One benefit of Amazon is the easy return process, so if you don’t like one of these you aren’t stuck.