And here is the answer. @mic was correct:
- As of July 3rd, 2022 to bus fare from 699 De Mayo to EZE airport
using line 8A air is 23 Peso. As of today that's less than US$0.18 at the official rate and less than a dime if you can get the "blue" rate.
- It's a whopping 95
stops and takes almost 2 hours.
- Line 8 has 5 "flavors" A, B, C, D and E. 8E (supposedly marked
"Autopista X") is apparently the "express" version and "may" be more
expensive. But I wasn't able to find one and I'm pretty sure they are
not going on Sundays.
- The experience is actually quite interesting and fun if you into this sort of thing. Avoid if you
- are in a hurry or have a tight schedule
- don't like getting up, close, and personal with the locals (which are quite friendly)
- have heavy or bulky luggage. There is no storage space on the bus
- have a sensitive derrière: the busses are fine but they are regular commuter busses and there are some impressive speed bumps.
- have a small bladder: there is no loo on the bus.
The fare structure is puzzling: even the shortest bus ride (5 stops) that I took cost 20 pesos and 23 for a 95-stop monstrosity doesn't seem a reasonable difference. It does make the "check in" process a lot more complicated and slower: you need to tell the driver where you are going so he can deduct the correct fare from your card. That can be challenging when you don't speak the language.
Trying to find where the bus stops are and when they come isn't easy. Google Maps seems to be the best shot. Some websites recommend Cuando SUBO but I found it to be very inaccurate and mostly useless. This being said, busses come quite frequently so in general it's ok to just show up and wait.