Bulk discounts for new domain registrations?

I have a feeling im going to have to go on a domain buying frenzy (50+) sometime in the next month or so and want to save a bit of $$$ if possible.

We currently spend between $11-15 per domain now at Joker but im looking to cut that down a little without having to use GoDaddy.

Any suggestions of where to look would be appreciated

Regards,

Lee