I wished I would have bought 6 cases(4 gallons each) of Valvoline full syn 5w-40 when it was on sale at O'reilly auto for $16.99 a gallon. However that was in November of last year and I've been trying to keep an eye out on that sale ever since.
06 F-350 CrewCab 6.0L, 4.10LS, DRW, FX4, short bed, moonroof, power slider, back-up sensors, black on tan heated leather
I always call around to the advanced, auto zone, oreillys, ect.. that are in bigger cities around me normally there prices are lower since they sell a lot more. Then I just take that price to my local one and they match it for me.