I was appalled to see parking places advertising 700 pesos for an hour in Once. That's close to 2 U$D/hour. 
The cheapest I found was 580 pesos. I'd rather park on the street, even if it is not allowed. Chances are nobody is going to give me a fine, especially since it is the same anywhere in that area.
Besides, the parking silos around the block, where we rent a fixed spot in the underground sector, is charging a staggering 24000 pesos per month or 64 USD. From Thursday to Sunday night, it is always full for nightly visitors going to the local restaurants for dinner and drinks.
