The long distance bus service in Argentina is top notch. You will find direct routes from the Retiro Station in Buenos Aires to just about any city in the country and the level of comfort and service is equivalent to a 1st class seat on an airplane.
When in Buenos Aires, tickets can be purchased either directly at the Retiro Micro Station in Buenos Aires or online using one of the wholesaler websites such as Plataforma 10:
If you are in any other city in the country, you can also purchase tickets at the city’s bus station.
Costs will vary depending on distances between destinations, but as a guide, you can plan on the bus ticket costing about 1/2 of what the fare is when flying.