Power Supply – $140 - Corsair 850 Watt Gold Rated PSU.
Motherboard – $95 – ASUS M5A97. This motherboard has two of the 16x PCI-e slots and two of the 1x PCI-e slots. All four slots can be used for mining GPU’s. If it is out of stock, this one or this one are good alternatives.
GPUs – $600 (3x $200) – AMD Radeon R9 270 - If the R9 270 is out of stock, the R9 270x costs just a bit more for slightly more hashing power and will still work with everything else in this setup. For specific configurationdetails be sure to read this litecoin mining hardware comparison.
Powered Risers – $30 (3x $10) Use 1x to 16x powered risers suspended above the motherboard with proper spacing for cooling the cards. You can get away with non-powered risers for rigs with up to 3 GPU’s, but I usually recommend going with powered risers if the price is similar as it reduces the strain on your motherboard.
CPU – $35 - AMD Sempron 145 Processor Since CPU specs have no effect on miningefficiency, we’ve chosen the cheapest option here.
RAM - $40 – 4GB Kingston DDR3 RAM
Hard Drive – $40 - 32GB Solid State Drive or boot BAMT from a fast USB thumb drive)
Case - $6 - Plastic Milk Crate (you might be able to pick one of these up at your local office supply store for less)
Power Switch - $6 – A basic Motherboard Power Switch does the trick, making it easier to start up your mining rig.
Extra Cooling - $30 - Box Fan (good supplemental cooling for a mining rig, as it pushes all that hot air away from the cards)
Operating System - $0-$90 - Windows 7 is my preference, but if you’re familiar with Linux you can of course download it for free (some folks consider Linux to be the best OS for litecoin mining, since it keeps your overall costs down, improving your litecoin mining ROI or return-on-investment). If you will be loading the operating system from a CD or DVD, a $29 external USB powered DVD drive will come in handy.
Monitor, Mouse and Keyboard (to install the OS and configure the mining software, no need to buy more than one set since you only use this for setup)
