Best advice i have:
Stay away from big box stores. Attempt to build one yourself, or have someone do it for you. Head to micro center with your budget in mind. Tell one of the reps in the Build Your Own department what you want to do. They will help you pick our some cost effective hardware. Bring it home and follow this guide: http://www.tomshardware.com/forum/274745-31-step-step-guide-building. Post to CR any issues you have.