Just received the Costco ad today in the mail and saw that, valid from 3/15/2018 to 4/8/2018, they will have Optimum Nutrition Performance Whey Isolate Protein (not regular Performance Whey, but Isolate) for $34.99. This is discounted from their usual price of $49.99. See attached picture of their ad.
Maybe your local Costco store still carries this, but mine doesn't (I live in California). If you have to order online, it is $1.99 shipping. This product is already online for $34.99 right now, and can be ordered immediately.
The link for ordering the product online is: https://www.costco.com/.product.705085.html
The flavors are as follows:
Chocolate - 4.19 lbs - 50 servings
Vanilla - 4.5 lbs - 55 servings
Now, I know that the picture on their website shows Vanilla as 4.08 lbs (for still 55 servings), but I recently ordered this at their full price of $49.99, and when it came in the mail, it was 4.5 lbs. This seems to be inline with Optimum Nutrition's actual product page, which is selling both flavors for $59.99: https://www.optimumnutrition.com/...ey-isolate
Oh, and not everyone needs Whey Isolate. Some people are perfectly fine with the cheaper Optimum Nutrition Gold Standard Whey Concentrate. I've noticed that as I've gotten older, however, that when I do my heavy squat / deadlift days, my body becomes a little lactose intolerant to Whey Concentrate, but yet it does fine with Whey Isolate. Less bloating and overall feels better after drinking it.