Costco is offering its members the 42mm Apple Watch Series 3 (Space Gray Aluminum Case with Gray Sport Band) for $309.99 plus $5 shipping. Opt for in-store pickup to side step the delivery fee. Apple charges $359 for this model and this is matching the Best Buy Memorial Day pricing from last week. Speaking of which, Best Buy has just about all things Apple on sale right now for WWDC. More details below. more…