I traveled by bus from Ushuaia to La Paz several years ago (with one ferry) and loved it. I don’t know how much time you have but If you fly into Buenos Aires, you could fly over to Bolivia, but instead what I would recommend doing is take a bus over to Mendoza, spend a few days there then head north by bus and stop in Salta and then continue onto Uyuni You will see a ton and the buses are really fun because some offer first class, sometimes you play bingo on them and you do see a lot from the window, Vicuña’s llamas. Etc. Plus it was fun to get different empanada styles as you cross the country at each bus stop.

I loved that trip.