|You've still got a ways to go. You're going to need a decent power supply, a case, the HDD, & a DVD burner. I don't what you already have so you may or may not need a mouse, keyboard, monitor, speakers, & the OS.|
Hard drive prices are still quite high due to the flooding in Thailand. A few months ago,1TB drives were about $50, now they're $150-200. Samsung, Seagate, Western Digital, & Hitachi are the big 4. Check the reviews before you buy.
Make sure to benchtest your hardware outside the case, it will save you a lot of headaches in the long run.