The problems with cases that are under that price point is that they usually come with a lack fo fans or really lackluster ones.

I would suggest something like the Enthoo Pro M (TG or regular) which is a really solid case. It comes in all black finish, has a lot of space for any parts, is well designed and actually comes with 2 fairly decent fans. You can buy a single fan to add as a second front intake if you want to or put it at the top for some VRM cooling since you will be OCing.

I do want to point out that cooler might have a hard time cooling the 8600K and its 6 cores once OCed. If you want something more stable, I would recommend the appropriate Scythe cooler or something like this Phanteks cooler.

https://pcpartpicker.com/product/gc8Zxr/phanteks-cpu-cooler-phtc12dxbk

Try this one. It has three RGB fans, Tempered Glass, and Mesh front for excellent ventilation.

https://pcpartpicker.com/product/6qPKHx/cooler-master-masterbox-mb500-atx-mid-tower-case-mcb-b500d-kgnn-s00

Cougar MX330 seems pretty decent for that price. It has a mesh front panel, PSU shroud, and a magnetic top dust filter, might be worth looking into.

I made some changes to your build and selected a case I think you will like. Updated the CPU cooler, better memory, better SSD, better PSU, better monitor.

Monitor has connectors that face vertical instead of horizontal which is easier on the connectors. It is VESA compatible in case you ever want to mount it on a stand with another monitor. Also, fully adjustable and integrated speakers.

PCPartPicker part list / Price breakdown by merchant