beginner heading to Everest - help me spend my money

Greetings all, I have had an F3 for a few weeks now which is my first "real" camera.  I have been reading a lot and have begun having fun experimenting outside of the auto modes, so I guess I would describe myself as an enthusiastic beginner.  I currently have the 18-55 lens with the 55-210 on its way.

One of my motivations for buying the camera is to have something decent for trekking to Everest base camp in March.  In addition to spare batteries, SD cards, etc. I could possibly budget up to $400-$500 more to make the most of the camera on this trip.  What do you experts suggest for someone of my experience?  My thought is maybe a decent prime lens or lightweight tripod/monopod for dawn/dusk mountain vistas, but being a beginner I would not trust my own decision making in these areas.  Any and all advice welcome.