As always with Costco the inventory varies from store to store and most places have sales tax. These aren't listed on Costco.com at all so it's a Brick and Mortar only deal
Costco's at least in Atlanta, Charlotte, and Spartanburg (SC) stores had these DVD sets for $24.99 each. There may have been some other complete series, but none that jumped out at me at a decent price (edit: maybe one other series). None of these are on Blu yet.

Roswell -- The Complete Series (17 discs) -- $24.99
Information: http://www.amazon.com/Roswell-Com...862&sr=8-1

Dead Like Me -- The Complete Collection (both seasons and the entirely forgettable TV movie) -- $24.99
Information: http://www.amazon.com/Dead-Like-M...025&sr=8-1

The Outer Limits -- Original Series Complete Box Set (Volumes 1-3 on 7 Double Sided discs) -- $24.99.
Information: http://www.amazon.com/Outer-Limit...143&sr=8-1

The one other possible set, but don't strictly hold me to this one since I didn't buy it:
Millennium: Seasons 1-3 $24.99
Information: http://www.amazon.com/Millennium-...341&sr=1-1