Cheapest 200$ PC build for casual gaming? (Terraria, Minecraft, ect)?

Also, I currently have a 500W power supply and a 500GB HDD that I intend to use again. My case would also probably be re-useable, although I'm unsure of its exact size. To replace my CPU, Graphics card, motherboard, RAM, and cooler, what price would I be looking at?

For your 200 you can get mid-range CPU. Or motherboard. Or really low end graphics card.

8GB of DDR3 RAM is about $50 these days.
A good mother board costs about $100.
A decent processor is anywhere between $80 to $150.
A "good enough" graphics card would he about $80 to $100.