Since you're in the US, I would wait till Nov 26th... Black friday... Sweet deals. WD 1TB for $59 and tons of others. Google for black friday ads and you'll be able to see the hdd's some places will have now.
You can buy one from Newegg.com
I use this one with my Wode and it works perfectly : Newegg.com - Seagate FreeAgent Go 500GB USB 2.0 Tuxedo Black External Hard Drive ST905003FAA2E1-RK