How bulk are we talking? Moniker will give you dirt cheap pricing ($6.75 .coms) if you deposit $500 one time. They're my registrar of choice. Also, namecheap can having decent pricing with coupon codes, but not as great of customer service.
Honestly, I am looking between the 5 and 10 range, maybe a bit more. That will definitely not end up being $500. I saw one website (domainpricedright.com) that sells domains for $6.95 for my range but I do not know if they are any good.
