Well, my gaming rig went down for a while, so I decided to bring back my old Dell Optiplex 755 from the dead. It had some very old components which had to be replaced. This renovation cost me $125.
CPU: The 755 had a Pentium 4 processor which was replaced by Core 2 Duo E8400. I'm quite happy with its performance.
Storage: The 250 GB HDD was already in there and it's not enough for me as I'm used to the 1 TB drive in my new rig. Still, I'm surprised it's working after I turned on my PC after about three years.
GPU: Bought this one from an old shop which was keen to get its hands off this. It's fanless and can't play most of my games but it worked nice when I overclocked it and was able to play Assassin's Creed: Freedom Cry and NFS: Carbon at an enjoyable FPS.
Motherboard: Its branded so it's a piece of hardware. I couldn't even install a case fan because it had no power slot for that and couldn't get a better GPU because it doesn't even have a 4-pin connector.
Other things which were already there is the PSU and RAM, which is DDR2. Anyways, I am quite happy with this and I can survive on this till I fix my new rig. I spent a lot on that old GPU, but I'm made of money. :D Over and out...