I'm assuming that you're with UA (or the employee is) - that's always good to know, since we have employees from many different airlines here

Enrolled friends are free in economy domestically or on flights from the US. If there are departure taxes, those are charged when you are leaving other countries. You can only check that by going through a listing and waiting to see what it quotes you, unfortunately. All that remains is imputed income - unfortunately, I don't see any way to look at that as of yet, but if you do let me know! That's always kind of an estimation anyway...