The 2-Packs consist of Kre-O Megatron and Sideswipe, or Starscream and Prowl. Both figure sets are shrinkwrapped together and come priced at $21.99 each.
The item # is 975771, so if you can't find it, ask for assistance and give them that number. Also, to save yourself a trip, here's the Costco store finder: http://www.costco.com/InTheWarehouse/Locator.aspx
An example store (Mayfield Heights, a Cleveland suburb) has them in stock: http://www.costco.com/inthewarehouse/detail.aspx?whsno=344 To see if they're in stock in your local store, find your In The Warehouse page and search for the item number. If it shows, they have it.
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