Regular flights are booked from Madrid (Barajas) to the International Airport in El Alto, La Paz and Viru Viru in Santa Cruz service provided by companies like Aerolineas Argentinas and Aerosur; the last one only offering the route Madrid-Santa Cruz-La Paz, while the others stop directly in La Paz; the cost could go from 1000-1200? to other higher prices depending on the class and duration. There are also less frequent flights to La Paz from other major European cities like London, Rome, Amsterdam, Berlin but they may have scales in other European cities before crossing the Atlantic.
From Latin America:
Other airlines that fly into Bolivia from other Latin American countries include LAN from Santiago via Iquique and from Lima. TAM Mercosur flies from Sao Paulo, Brazil and Buenos Aires via Asuncion. Copa Airlines has begun to fly to Santa Cruz from Panama City. Gol Airlines and Aerolineas Argentinas also fly directly to Santa Cruz.
From the USA:
There are departures from Miami to La Paz and Santa Cruz on American Airlines, and the Bolivian airline Aerosur offers flights to Santa Cruz and Cochabamba with connections to other Bolivian cities. Once you have your international flight booked, it's far easier and cheaper to organize your internal flights from the point of departure.