Adorama offers the Canon Pro II Super High Gloss Photo Inkjet Paper 4″ x 6″ 100-Pack for $24.95. Buy three packs (300 sheets in all) and the price drops to $14.95 in your shopping cart. With free shipping, that’s the lowest total price we could find for this quantity of this paper by $63. (For comparison, most merchants charge $25 or more for a single pack.)
Update: Link corrected.