I didn’t look carefully, but sometimes I go on the website before going to the store and most things seem to be 50-150NT cheaper in person. A cab ride back isn’t going to be more than a few hundred NT, so it’s quite a mark-up if you’re buying a lot at once, but I don’t blame anyone who’s willing to pay extra to avoid the insanity that is those stores on weekends (or just doesn’t want to trek out there)
I’ve never actually used the online shipping from Costco but the credit card is super easy to get. They wanted a picture of my bank book showing a balance of at least NT40,000 and sent it to me within a week. For all the hassle that credit cards are for foreigners, this one is the only one I’ve tried to get and it was no problem. I have a work-based ARC, if that matters.
Ruten might also be an option, but my understanding is that the Costco website mark-up is because of “free” shipping, so you’re basically paying 50-150 NT/item delivered and that’s that. But you’d have to do your own math based on what you’re buying.