The $40 Case: Cougar
I bought a few of the Cougar MX-330-X cases over the years. I even have their glass side panel one, MX-330-G, for my main computer (daily driver).
It is sold on Amazon.ca and Walmart.ca for under $40 with free shipping. It is the cheapest full tower ATX case I have found.
It gets sold out very quickly on Amazon.ca every time I look it up.
It comes with one 120mm black fan with 3-pin connector and enough screws to mount all types of motherboards (ATX, mATX, and ITX) and other accessories. It has enough 120mm fan spots to mount 7 fans to cool. There is absolutely no complaints when you get a case this cheap. It also has a 5.25″ drive bay to mount a DVD/Blu-ray drive.
The only minor problem is the expansion slots screw hole. You have to tighten just enough and not over tighten using fine screws. The metal is so thin that you can strip it easily. If you do strip it then you must use coarse screws to make a bigger hole to hold the PCIe cards. After this fix, don’t strip it again! I striped a few LOL!
Anyways, I don’t bother with expensive cases no more. Like this has enough ventilation to cool most things I think and water cooling radiator support.