No Costco close to me, but it's still pretty early for our nurseries and garden centers. I've only seen one greenhouse going up at the local Hy-Vee. Not sure why, but there doesn't seem to be a big variety of Dahlias in our area. I know it's too cold for them in the winter, but there are people like me that are willing to dig them and store them. I agree that the shipping would be expensive for different online retailers.
Rose