Going to atm you get hit with ATM fee, best rate other than Western Union is in Orange Plaza. The difference is usually .10 but do not need passport and do not have many eyes in what you are getting. Please though if go, do not treat the guy like he works on the street corner. I watched an American count out 23000 peso at window out loud only to miscount twice was a very bad look. This guy cashes personal checks up to 10 grand, he deals with the heavy hitters in Sousa he is not going to cheat you out of a couple 100 peso.