Well the ASRock board I reccomended is 100$. That leaves you with 400$ for a CPU cooler, a decent case, RAM, a PSU, and an optical drive (if you need one). Thats plenty, but not much for a good graphics - you may either need a board with onboard graphics, or buy a cheap graphics card - something like a Radeon 7770. Thats about 150$. That, a 100$ motherboard, 40$ RAM, 60$ case, 60$ PSU. That leaves you with 90$ for a cooler and optical drive!