Adding Hard Drives
I currently have 2 SATA Seagate Barracuda hard drives (1x 140GB, 1x 80GB). Over the years, the 200GB isn't nearly enough, so I'd like to upgrade to at least a terabyte. I'm in the market for 2x 400GB (or higher) SATA drives, and after missing a 400GB drive for $50 deal on slickdeals, these things are definitely more money than I had expected. Not only that, but a user on another forum tells me I have to upgrade my power supply as well (I currently have a 480W). Wonderful, as these are also more money than I had hoped.
Using the power supply calculator on antec.com, I'm told that I need 515 watts of power. Who knows how accurate that thing is; plus I skimped on some details that I didn't know the answers to. I know nothing about power supplies, and very little about hard drives. What do I need to know before purchasing a power supply? Is 515W an accurate estimate; are they one-size-fits-all; is there a limit on what my motherboard can handle; etc.? Keep in mind, it's highly likely that I'll be adding things like external drives sometime down the line.
Also, is there any way to avoid spending nearly $360 on 2x 400GB drives and a power supply?
Thanks in advance and I apologize for my lack of knowledge regarding this.