Costco doesn't sell diesel (and I looked over at Sam's some years ago, but found no diesel pumps - maybe things have changed?).
The best I can do is to continue to maintain my Tactical Diesel Reserve where I can store 3 to 6 months of basic usage and recharge the reserve as lower prices present themselves.
Maybe I should frack in the backyard?
I bought it at $2.05 yesterday
Brand new Costco has diesel here in Torrance, Ca.