Target via eBay offers the Up & Up Diapers Giant Pack for $19.99 with free shipping. That's $9 off list and the lowest total price we could find, although we saw it for a buck less last fall. It comes in sizes 2 (172-count) to 6 (104-count).
Target offers two Up & Up Bulk Plus Pack Diapers bundled with a $25 Target Gift Card for $75.98 with free shipping. (Add two to your cart to see this price; the gift card will display in your cart.) Assuming you use the gift card, that's $25 off list and the lowest total price we could find. They're available in size 3 (222-count), size 4 (192-count), or size 5 (172-count). Deal ends May 30.