Let's get the bus ticket to Bolivia

Two day later Damian calls me, and asks me when can we go to buy the tickets, to my answer "this afternoon is good for me", so he picked me up from my job and we went straight to "Retiro Bus Station". That is the main bus and Train Station in Argentina, from there buses going all over the country leaving every minute....
So we go to Retiro park the car and get in, looking for our bus tickets, without really knowing even to where should we travel to cross the border (walking with our backpPublish Postacks) to Bolivia.
We asked in some of the companies until one girl from the other side of the window explained to us that we had to buy a ticket to La Quiaca in the Jujuy Province(see map) and from there take our backpacks and cross the border to the first city in Bolivia called Villazón through a concrete bridge where you can make customs and migrations.
So let's do it, we bought our tickets (one way, because backpackers never schedule!!), we paid around $125(around 40 US dollars) and that was it!!.
Then I looked to Damian and he looked at me right in the moment when internally I was asking to myself if this was a good idea, and I knew he was asking himself the same question.. two backpackers that barely know each other going on a two months trip...
Anyway we had our tickets, so there was nothing else to be done.... or maybe lot's of things...