Arriving by plane in La Paz you can reach every Bolivian city by bus. The municipal bus terminal is easy to find by asking peolpe for "Terminal de Busses”.
Oruro beeing the closest like 2 hours and half, Cochabamba from Oruro is 4 hours, I assume from La Paz it is more.
And from Cochabamba to the tropical city of Santa Cruz is the longest like - 12 hours, you can always take a plane if you are in a hurry, in 1999 I paid some $60 dollars. Still relatively cheap.You will enjoy the weather of Cochabamba, reminds me of the weather of California (Around Oakland) the weather in Santa Cruz is real hot like 90F or 35C on Summer months like February.
Oruro is a cold city but enjoyable during the time of the best Carnival of Bolivia, which takes place in february and is a folkloric parade, that lasts like 12 hours on Saturday, with more the following day. It is loved by tourist all over the world it is unique.
