We get near Costco often enough that we rarely buy elsewhere.  Last bought there on Friday at $3.09.  With my Costco Visa Card I get 4% cash back, so at $3.09 the real price is $2.97.  Closer to home prices $3.27 to $3.43.  There's one station about 1/4 mile away from Costco that usually has gas at the same prices as Costco.  There's a Sheetz station pretty much at the entrance to Costco selling at $3.25.
Costco recently installed a couple card readers to scan you in.  They usually have two "checkers" who take a quick look at your cart when exiting, but it rarely delays you much at all on leaving.