I would go get a really crappy desktop and then purchase USB Scrypt Asic devices and run them off that computer, save your money for a nice gaming computer for you to use and not ruin the graphics cards, due to their lessening efficiency when it comes to hashing power and cost to run.
Crappy desktop is around $100++ And the amount of power used to operate it wouldnt make it even profitable. Buy a raspberry Pi instead, uses less power, less space.