After the 4th wave of upgrades, this is the end result.
I previously had an i5 4690 (non-k) running with 2x R9 280x in crossfire. Now that the two R9 280x's have been replaced with two R9 290s I've decided to put an i7 in the build for better performance. I saved a lot of money by buying 2nd hand parts. I was very careful, only buying parts that still had warranties. I saved a lot of money by selling my old parts and buying 2nd hand. If I had bought everything new it would have cost me $1035,-. By buying 2nd hand I spent $730,- and by selling my old parts I gained $470,- so the total cost of the upgrade was: $260,-.
I also Salvaged the 100Gb HDD of an old laptop that was just laying around at my parents house. I backed up the data, I whiped it clean and installed windows 7 on it. Since old games (like Rome Total War, C&C Generals and Homeworld 2) simply don't run on Windows 10, I can now restart my PC, boot up Windows 7 and play those classic games.
All in all I'm very happy with the end result. I can play every game, maxed out with at least 60 fps on 2560x1080 (which requires about 30% extra rendering, so on 1920x1080 I get at least 80 fps).
My apologies for the bad picture quality, I had to make them with my phone, which doesn't have the best quality camera.