i call around different dealers to check their prices. if there are a couple dealers near by, at least one will sell it without much markup. most will order for you if they dont have instock. usually theres coupons floating around. with 20% coupon i got for parts and accessories, i got Mazda 0w-20 with Moly for around $6.80 per quart. if youre gonna pick up oil, might as well pick up some tranny fluid if you plan to change any in the futures.
@mrchowmein has a good point. I got a cool parts guy at the dealership once and he charged me the same price as the websites for MS3 oil filters, so I bought 5 of them. Just depends on who you talk to at the counter.
I use Tasca Parts | Lowest Prices Anywhere for Genuine OEM Parts. Normally I purchase 6 oil filters and three air filters at a time. We have three Mazda 3's with skyactiv engines in the family. Un fortunately the 2014's cabin air filter is different than the 2012's. I have also purchased replacement body parts for the 2013 Mazda 3 that I traded in for the 2014. I hit the remnants of a blown truck tire lying in the middle of the lane square on and ran over it. Couldn't change lanes because of traffic. Happened so fast. Ripped the bottom covers and left fender splash guard off. Pissed me off but at least I'm still here. Could have been worse.