I discover BA Street Art Walking Tours by chance, and I must say that the decision to take the tour was really great! Matt was an excellent guide, explaining all the graffiti in a very professional way, you can guess he do love his job! I recommend everybody visiting Bs As to consider this tour as it will be really a great experience. Moreover, if you're lucky, you can have the chance to see some artist at work!
The tour price was Argentina pesos 75, quite cheap for what I got.