There are ATMs at both airports. Keep in mind that ATMs in Argentina tend to charge high fees - this doesn't bother me, as I have a Schwab debit card that reimburses me at the end of the month, but it should be noted for those who don't.
That said, I'd recommend bringing a couple of hundred USD in cash, just in case. Sometimes the ATMs don't work; sometimes they're out of cash... I actually have had more problems with the machines at EZE than I have with random bank branch ATMs located on city streets. Probably because the airport ATMs are used a lot by people stocking up on pesos when arriving in the country, and the banks don't fill them enough.