I would visit Yavi, it is a town lost in time... really nice as an experience when looking for no tourist but interesting places... From La Quiaca you cross to Villazon in Bolivia and there are trains available to Uyuni... here're schedules
http://www.fca.com.bo/Servicios_arch...itinerario.jpg -Spanish- and prices in the Bolivian currency (Bolivianos). In Uyuni you can find the greatest Salt Flat. Bolivia is safe and cheap, accommodations are simple but you can find good places, food is good but you have to mind the altitude and cleaness... hope that info helps... cheers!!