As above, you get what you pay for.

$300 will get you a run of the mill no name Taiwan / China made chair sold out of places such as Office works.

I endeavoured with shit chairs for years and then forked out for a properly fitted chair from Chairtech in North Perth.

Was keen on an Ergo Human but the mesh was too light weight for me. Ended up with an Artia Venus Executive and almost 2 years on, it still feels new and I have more than enough thigh support (which I found lacking in other chairs).