Non-U.S. Writers and Promotion?

What can writers do if they're based outside the United States?

A reader asks:

For those of us who don't live in the US, what sort of marketing can we do? Is it worth spending the money on a trip to the US for book promotion?

I’m going to assume we’re talking something on the level of an intercontinental flight and not a Canadian writer who is contemplating a U.S. con a few hours’ drive away. If we’re talking pure mon…