I have a suggestion;
Take the BB-cost of the foreign provider, include the trans-
oceanic link, add this to the BB-cost of the US peer and
divide the sum equally.--Peter
To which I have my standard response to you, Peter 
The unfortunate reality is that most US customers wouldn't notice or
care of connectivity to Europe went into the crapper.
This does NOT mean that we don't have to think about these issues -
but since it's cheaper for many Eurpean backbones to connect to each
other by coming to the US anyway, I really don't see most US providers
stretching hard over either ocean any time soon.
Avi