I would stick to Nokia's ecosystem (current) since you're going international, you need their Here Maps, Here Drive, etc. Download any latest maps to any country you're going to. And if you're in the US, go with Tmobile since their data is free international if I'm not mistaken. Not too sure about Blu Win, but if it only has basic WP features, u wont get much out of it.
Lumia 635 is about 150 right now.