Yes Costco has nice price for watches. But you are looking at two completely different model. "You get what you pay for" in watches is true. Nighthawk and Skyhawk model are super accurate compare to the one you bought. Pilot, military, and navy people are the likely people who want Skyhawk model that's why it's more expensive.
Also Sapphire and Titanium is just the exterior of the watch, the internal cost a lot more.
Actually both mine and this Skyhawk are A-T models and all A-Ts are equally accurate because they sync to the same radio signals.
I have to disagree with you on the sapphire: personally I think anybody who spends >$300 on a watch without sapphire face is wasting their money. Wear any mineral face watch for several months and you'll be weeping at a badly scratched piece you bought for $300.