I have OSDE 210, the most basic OSDE plan. Since I'm in the youngest age bracket (18-25, valid until the day you turn 26) it's ˜400 pesos per month. The price has gone up 15% twice in the past year, and will surely keep going up next year. They all will, but I can't complain since it's still incredible compared to the U.S. healthcare system. The older you are, the more expensive your monthly payment will be. My boyfriend is in the next age bracket of OSDE 210 and pays about 510 pesos per month, for example.
I've been pleased with it, but do research what is covered. For example, my boyfriend just got ACL surgery and that and all pre- and post-surgery consultations are covered, including his overnight stay in a private room at the clinic, but he had to pay for the knee screws a la carte, that or go up to plan 310. They were 3750 pesos--ouch. 50% percent of the total cost of the screws, since they were imported.
The process was quite simple. I went to the OSDE branch at Corrientes y Reconquista, took a number, and was called to a representative's desk in 5 minutes. He took my name, passport number, and asked a surprisingly small number of questions (do you smoke, what surgeries have you had, etc.) I left with an official signed slip of paper to carry in my wallet stating that I was covered effective immediately. Didn't pay a dime. A few weeks later, I received my first bill in the mail. They will prorate it. So for example, if you start Oct. 7, they will not charge you for the entire month of October. You must receive the card in person. They will not just drop it in the mailbox. You can request that they send it to your place of work if that's easier.
Unless you have a chronic health condition, I'd say start at 210. If something happens, you can always move up in the plan. They don't really punish you for pre-existing conditions like they do in the U.S. As someone who has used her insurance for everything from general checkups to emergency room visits to free birth control pills to cardiac surgery consultations, it gives me great peace of mind.