n/a, the sellers on ebay/Amazon buy in massive bulk from Costco and earn pennies on each sale. That's the reseller business model in a nutshell. The prices almost doubled overnight on Amazon and Ebay because they now have to deal with the same restrictions. That's where I usually go as online wasn't much more than in store. I saw the sky high prices and figured I'd stock up at Costco. Then at Costco I experienced the limit - which made sense and correlated with the increased online pricing.
I haven't been able to find anyone that comes close to Costco's price per pill. They are the gorilla of the immodium sellers.
I'd love to send a complaint to Costco but I doubt anyone who mattered would see it. It's unfortunate.