For some reason I stumbled upon this thread and just to clear something:
Ampere and Wattage is something important but in this case nothing he should be worried about.
I run 16 harddrives myself since two years back on an Aspire 500w and no problems here. Stable all over and its an overclocked system with two raid5 setups and a decent graphiccard.
I run my system in a chieftec fulltower maxtrix style and got no problem with temperatures.
About the prices, the 500gb disks are about 4x more expensive here in Sweden than compared with the 250gb and 300gb- disks so we are on the same setup here. 6x200 and 8x300 plus 2x80gb in raid1 as systemdisk
Hopefully you are up and running by now. Id be interested in what kind of setup you went for after asking here. Also remember that no raid, regardless of form, is here to replace a real backup!