You mean the cost of a taxi? GRU taxi service (Guaru Coop) is very reliable and efficient. A taxi ride from GRU to Hyatt hotel will cost you about R$110 and Guaru Coop accepts all major credicards. It will take about 40min depending on time and traffic. Guaru Coop operates with fixed price and no meter, you will pay before you board the car at the taxi's company kiosk.

http://www.guarucoop.com.br/eng/index.html

Another alternative is the Airport Bus service which charges about R$35 and stops in front of the hotel, it will take about 1h of journey.

About money exchange, I always withdraw money from one of the ATMs with my Dutch-issued bank card so no hassle of rates or commissions. I guess rates at GRU will be better than if you exchange money at the counter of Hyatt hotel...

Rgs,