Have you considered doing Booster Cases? Perhaps deeper discounts could be offered for an even larger quantity. Booster Cases contain 6 Booster Boxes, or 216 Booster Packs. The Packs alone would cost $864, but they generally retail for around $600 for a Case.
The prices you are getting for these Booster Boxes would make a Case cost $489 (at $81.50 per box); but people who want more cards would surely be interested in saving even more; perhaps $450 per Case, or less!