Hi all.
Caleb, here's an idea. I believe that Apple uses the Seagate brand of hard disk internal to the G5. You could start your research with Seagate and see if you could get cost effective Seagate SATA drive.
While some will say don't use Maxtors or other brands, any disk of any brand can fail at any time. However, I solely use Maxtors, and I have never had a problem in the many years I have been using them. I guess good disk practices help as well.
I would use pricewatch.com and shopping.yahoo.com as places at which to search for decent hard disk prices.
Good luck.
Take care.
-DH