You'll should be specific about the kind of experience you want from your build, but here's an example. A low-end build including: an Intel Core i3 CPU/Mobo combo will cost you about $200, a mid-range NVidia card will cost you $100 (GTX750 1GB), 8GB RAM will cost you $60, and a 120GB SSD will cost you $60. That leaves you $80 for the power supply and case (do-able). I assume you have some spare parts around to put into the build, and either an old HDD or external HDD to use for file storage. This won't be a rock star build but if you don't mind gaming on low to mid graphics in SL, it'll work.