If you are willing to pick it up at the local store, you can get free shipping to the store AND the $20 dollars off. If you buy two of the 300 rounds packages and use the $20 off it is $195.28 including sales tax. That works out to 32.5 cents per round with the Dry-Box being lagniappe.
If you have additional e-mail addresses you can get and use multiple $20 rebates if you place separate orders using each rebate.