No Costcos here, & I refuse to pay Sam's money for the privelege of paying them more money!
Look for alkalines on sale. I watch the Sunday paper sale ads & local supermarket ads & buy alkalines only, usually Walgreen's house brand on sale. When they run sales Walgreens has good prices on AAA, AA, C, D, & 9V, & I find their house-brand alkalines to be very good batteries. OR: Sometimes Brookshire's puts the Panasonic alkalines on sale cheap($.59 to $.79 per 4-pak in AA & AAA) & I buy the limit(usually 4 pkgs) on those.
As far as paying the big $$ for big brands like Duracell or Energizer- nope, haven't done that for *Many* years.
**Note: Alkalines can have a very long shelf life. I'm still using Ray-O-Vac Alkaline D-cells I stocked up on in 2001 or 2002 when batteries, coleman fuel & lamp oil became available again after our big ice storm.
They don't last as long as new stock, but they last a lot longer than you might think. My big GE SuperRadio(6 Ds), the often used old Sony boom box(4 Ds), & my red 3 D-Cell Maglite(bulb, not led) still go for ages on 'em.