I spent months dithering over my latest ebike purchase and I already had an ebike to ride, every option seems to have some negative facets to it. How much time do you have before you plan on leaving for your trip?
When I got a quote from them the Xiongda 2 speed motor kit was remarkably inexpensive for shipping to the US compared to what I see companies like bmsbattery ask for and the kit itself was fairly reasonable too. If you have to climb through the mountains and then do a lot of flat cruising I think you should look into the Xiongda seriously as an option.
You can email Yona, a customer service person at Xiongda, and she will get back fairly quickly with a quote including shipping if you tell her what you are looking for, voltage, front, rear, wheel size, what sort of controller, throttle, pedelec, display and so on and your location of course.
yona@xiongdamotor.com.cn
http://www.electricbike.com/2-speed-e-matic-xiongda/