For general purposes, for something that is recent I try to take a look both at retail prices and subtract between 25-50% based on demand as seen on other sites selling used items. For instance, might check eBay or other used retailers and see how they are pricing like items.
Here, using CL is basically a giveaway or sit on it situation. There aren't any buyers paying "worth" for anything. I find that the bay tends to be a bit overpriced for most items.
In my opinion on this, your GPU is by far the most valuable and desirable item. The HDD is a serious detractor. According to the case and it's looks (windowed, etc.) I might suggest that you buy a cheap SSD, put on a clean install of OS, advertise it such that the storage is on HDD, perhaps even add a cheap LED strip to two, and run it for ~500$ according to your market and sales device. My personal thoughts are that you could readily get $250 for the GPU alone. The i5 and mobo could possibly pull a bit over $100 together....so according to the other peripherals and the demand in your market I would adjust from there.