There's free 2-day shipping from Costco for purchases over $75 (at least in Seattle). It's not hard meet that requirement. Right now, I only tend to go to Costco if I need to buy refrigerated or frozen items.

Yep, around 18% higher not including tip, in my estimate. HEB (local Texas grocery chain featured here a few days ago) puts in just a 3% margin for pickup or delivery (before tip.) Walmart and Sams have no special delivery/pickup margin but instead charge delivery fees that can be avoided by membership levels or order amount thresholds.

But saving the cost and time of you driving there yourself, which if you're honest is probably worth the delivery fee.

Sure, although personally the comparison would be to delivery from other stores.