The currency in Los Cabos is the Mexican peso (MXP), though prices are often given in U.S. dollars. At this writing, US$1 was equivalent to approximately MXP 10.8.
Even if a currency-exchange booth has a sign promising no commission, rest assured that there's some kind of huge, hidden fee. (Oh.. that's right. The sign didn't say no fee .) And as for rates, you're almost always better off getting foreign currency at an ATM or exchanging money at a bank.