All buses leave Ataco from the corner of 2a Calle Pte with 4a Av Norte. Buses are frequent and one was just leaving for Ahuachapán as I arrived. It took 20 minutes and the fare was 0.40 dollars. In Ahuachapán the bus stopped near the market and I walked about two blocks through the market to get to the bus to Tacuba. I sat on the bus for 20 minutes before it took off. During that time there was a constant flow of sellers walking through the bus selling snacks, drinks, torches etc. The bus left on time at 12.00. To Tacuba it took 40 minutes and the fare was 0.65 dollars (June 2009). In Tacuba the bus stops along the main street, a few blocks up from the main square. It was not far to walk to Hostal de Mamá y Papá where I was going.
There are two direct buses from Barra de Santriago to Sonsonate. One is leaving 4.30am and the other at 12. I took the 12 o'clock bus which was leaving from the end of Calle Principal (the same place where I had been dropped the day before). The bus left on time and it took 1,5 hours to Sonsonate. The ticket was 1.70 dollars (June 2009).
At the terminal in Sonsonate I bought water and asked for a bus to Ataco. Ten minutes later, at 13.40, the bus left for Ataco. It took quite some time before we left Sonsonate as the bus stopped to pick up more and more people.
The bus was another of those old school buses where I could have my luggage just in front of me. To Ataco it took 1,5 hours and the ticket was 0.75 dollars (June 2009). In Ataco the bus stops just by the market.
As tourists you will likely be going to Ataco by bus, taxi or private car. Taxi is a reasonable choice if you plan just to stop by or stay only few hours. At time of my visit there were no taxi stands in Ataco and you will need having your outside taxi waiting for you. I hired a taxi in San Salvador to take me to the Ruta de las Flores - and therefore among the other villages to Ataco - and agreed on a US$10 per hour fare, though I suspect I might have negotiated harder.
To get to/from Ataco, the alternative to private car and taxis is the bus. Bus line to Ataco is the one which serves the Ruta de las Flores and that goes from/to Ahuachapan to/from Sonsonate stopping in the villages on the way. If coming from San Salvador you shall get to Sonsonate first and then take the bus to Ruta de las Flores.
Buses operate with high-frequency during the day hours two to four times per hour. Price is few cents of US dollar per ride. Buses will drop you a couple of blocks off the Main Square, right in the center of Ataco. There is no night service and if you end up staying in Ataco after 7:00 pm most likely you shall overnight.
I did not take the bus and I cannot say whether it is a comfortable ride. I suspect it is not (see photo attached, the service is operated with dismissed US school bus equipment), though I am sure it is an interesting experience.
There is also a minibus service (see other photo attached) which make the same trips in about the same time at about the same rates.
You don't need anything else but the soles of your shoes to get around Ataco, but in the event, you will find mototaxis for hire in the Main Square.