If you look up the cheapest US shipping rates you'll find they're roughly the same range, and that almost all the comparisons purporting to show otherwise are cheating, typically by using retail pricing on a more expensive shipping option.
>So he turns to his shipping guy. And he asks, how much would it cost for us just to ship this mug, like, not across the ocean, just across the street?
>SMALDONE: He told me it's going to cost us about $6.30 to ship this item.
Amazon page for mighty mug says it's 12.6 oz shipping weight. https://www.amazon.com/Might-Mug-1525-Mighty-Black/dp/B00FZD...
Round up to 13 oz, then look up rates for the cheapest shipping option for packages under a pound "parcel select lightweight". See https://pe.usps.com/text/dmm300/Notice123.htm#_c139
The cheapest rate is $2.02 for 13 oz. This rate applies when mail is injected at the closest mailing point (DDU), which "mailing across the street" corresponds to.