We had to withdraw money from an HSBC ATM nearby. Maximum is 3000 pesos and you pay extra 176 pesos fee to Argentinian bank. (plus whatever your bank charges extra on top of if)
Then tube from Bulnes to Retiro station. There are not enough signs where to find Omnibus terminal. Before you get out from the underground station, there in one arrow pointing to Omnibus terminal, but outside, there is nothing. It took us while to figure out that you have to walk quite far, passing one or two train stations, before you get to bus terminal building. Just stay on the same side of the road as you get of the tube station and walk. The omnibus terminal is big and the tickets are sold on the second (top) floor. We read (in some blog) that La Plata till is number 5 (there is about 200 of tills). We waited until someone showed up and tey told us, that we have to use the SUBE card to get to La Plata. They don't sell tickets anymore. So simply charge your Sube card with enough money and find bus number 195. It the terminal, there is a map (on the first floor) with bus numbers where you find them. Don't try to follow numbering outside - it doesn't go from low to high numbers, it seems pretty random.
I charged my SIM card with 150 pesos and got to the bus stop. Dos boletos a La Plata por favor. 38 pesos per journey. The driver types it on the machine, it displays 38 on the touch point, I touched with the card, waited to see 38 again and touched second time for my wife and job done. I'm not here how long was the bus ride. But about 1 hour.
In La Plata, the bus stopped next to the train station as a first stop, but it's better to stay on the bus, it gets close to Plaza Italia, stops next to some pharmacy. Then we walked from Plaza Italia, following Avenida 44 and Diagonal 74, to the big square with the Cathedral. Visited the cathedral for free, then got pizza in Pasillo 74, back on Diagonal 74. Pizza grande was 240 pesos, and enough to feed bot of us. We could pay using Visa debit card.
After the lunch we went back to cathedral, but to the museum, to get to the viewpoint from the cathedral tower. The museum entrance is 60 pesos, there is nothing to see. The cathedral is quite new. We went to the museum just because of the view from the tower. There is a lift which takes you to a floor near to the top, they give you few minutes to look around and then they take you to the very top. The lift is really new. And the views from the cathedral tower are not that good, because you cannot get close to the window - there is a glass window half a meter away from the wall edge, so you don't see that much.
Then we walked to Museo de La Plata, using Avenida 53. The street was really nice. A lot of trees in the middle of the street all the way to the park with the museum. The museum entrance was only 40 pesos per person. In the museum you can see nice display of dinosaurs. Not many tourists at all.
The way from the museum was rather tiring, took us maybe an hour to get to and find the omnibus terminal. In the reminal, there is maybe 5 bays for buses going to Retiro, just with different stops on the way. We took the one via Autopista, paid again 38 pesos and got to Retiro. There we wanted to get another bus to our accommodation and we couldn't find the bust stop for bus 108, so then we took the tube to Scalabrini Ortiz and walked home with a short stop in Carrefour for something to eat