I just wanted to post on here saying that I am so grateful to all of you. This thread (along with http://www.head-fi.org/t/627036/sennheiser-hd580-hd600-replacement-driver-parts-lists-costs) showed me the process of buying replacement parts and helped me to buy all the spare parts I needed (650 drivers, 600 grills, 600 headband, cable, earpads, and lower trim) to make own pair of headphones! I will call them my 625s!
Anyway, just signed up with Head-Fi to tell everyone about my experience and that it can be done! Total cost: $269.18
I'm listening to them right now and couldn't be happier.