Ba lover,
I think that you can both travel on foreign passports therefore dont need a permit to travel as both you and your baby come under US jurisdiction. What makes you think you need a travel permit? Unless of course you came into Argentina on your Argentine passport. I suggest if that is the case YOU go to Colonia for the day re-enter Argentina on your US passport. Then when you leave with baby you both leave on your US passports. If they ask why baby has been in the country longer than you just say Hubby came in before and you with baby. I do not think baby comes under Argentine Jurisdiction. But as you are Argentine they may get crabby. Yeah, thats it! go to colonia, get your passport US stamped coming in, then do a dummy run together at Buquebus just to see what they say, if it works all go to Colonia and then you all return on US passports with equal dates on them and never get stuck in the system with the bloody documents. Once in the sytsem its like a a trap you never get out of.
hope that helps
oh!d if you do need a escribano I know a fantastic chap in Buenos Aires, he's darling he has done some other legal work for although I used a local Escribano for my permit here in Pilar. The chap in BAs is, Ponciano Vivanco. I had my cell stolen last week so will have to search for his number.
One thing I will say is that he is as straight as a dye, not in the square sense but in the moral one. He would never rip you off.
Oh yes, my last document cost around $300 and that was june 2006.