I'm not saying let your local shop gouge you
What would you do if you fouled your last plug, your buddy grabbed the last bottle of mix and didn't tell you, a cable broke 5 minutes into the ride on the first sunny day in three weeks and your local shop was not there?
Well, in my experience, unless you had prepared for that cable/plug/bottle to expire or run out, then you're SOL because the shop won't have it in stock anyway. I can't believe the amount of times I've had to order consumables....it's just easier to go to the internet and have it delivered to my door rather than spend two trips to the bike shop that's 25 miles away (one to order it, the second to pick it up). The ideal place is Cycle Ranch, a track no less, that carries more inventory than any bike shop I've been to. VERY impressive.