I posted this question 6 months ago so it may still be in the archives somewhere. I ended up getting mine from a shop I just found in my local area (downtown). I think I paid around 30 pesos for 100 then. The main problem I found was they dont use a particularly good quality card.
I got mine printed at Grabatto - you can design your own card and pick out the card stock. They have a bunch of locations - I had ones done in Alto Palermo and Solar in their stands. I had personal cards printed there and they did a really nice job. If you don't require anything super special, they'll usually print them within an hour or two.
I'd recommend going with someone who can do offset printing, you'll get a much better deal. There's a place on Bartolome Mitre (3700ish) that does 1000 for $90 pesos, and I got quoted $140 for 1000 (I think) at a shop on Medrano, around Guardia Vieja.. there are tons on that street. I wasn't too happy with the paper of the one on Medrano, but it wasn't bad, and I haven't seen the ones from the place on B. Mitre. If you want fewer than 1000, they can do digital printing, but I'd still go with a place that has offset capabilities, as their printers will prob be better in general. And they should be able to handle an Illustrator file, if not, you can save it as a pdf or eps and they should take that (never know what version of illustrator they'll have..) also remember to convert all fonts to outlines!