I'm trying to find a flight from the northeast (Boston or NY) to La Paz in June. Expedia has the best fare (approx. $830), on LAN, with a connection in Lima. I've read a lot about base fares, base plus, etc. When I book on Expedia, should I assume that it's the appropriate fare (in other words, not the base fare)? Or is my Expedia fare not guaranteed and I could still be hit with the $170 fee?