The hostel I was staying at offered La Ventana for I think 190 pesos if you were a member, and 220 pesos if you were not a member.

Based on my dining experiences elsewhere, I'd say the dinner and wine were worth at least 100-120 pesos altogether. The transport is maybe worth 30 pesos. The venue is quite elegant. I don't doubt that you get a more authentic version elsewhere, but this is an enjoyable evening. As mentioned, the guitarist is excellent.

I also did La Boca Tango (which I can't find a link for online). The dinner was not quite as good here, but still fine, and the wine did not flow quite as freely (but I had more than enough). This features a cute operetta held out in the courtyard, and then a regular tango show. This was enjoyable too, and a little cheaper than La Ventana.