There are 1.232 kilometers from Buenos Aires to the city of Neuquén, you can choose the bus or the airplane. By bus the ride take 15 hours, and by plane 1:35 hours.
Round Ticket by bus: 180 pesos ( u$s 63)
Company: "Transportes Via Bariloche" , "Chevallier", "TAC", etc.
Bus Frequency: at least 8 per day
Round Ticket by plane: 430 pesos (u$s 150)
Company: "Aerolineas Argentinas", "Southern Winds"
Plane Frequency: 4 per day from monday to friday, 2 on saturdays and sundays.
Every days a bus departs from Neuquén city to Caviahue, acceptable quality services with almost new units. "Centenario" is the name of one of this companies, "El Petróleo" is another one. Low prices tickets for a 320 km ride to the volcano Copahue.
Here i give you the telephone number of Centenario Bus Company and El petróleo Company below