I took a taxi from GRU to CGH last month and the cost was R$110 or about USD65, there is only one taxi cooperative (GUARUCOP) which operates in GRU, service is excellent, you can pay with credit cards, however, fares are high.

I arrived with AZ at 4.20am, boarded the taxi at 5.00am and arrived in CGH at 5.15am, and took my flight to NVT at 6.00.

If you have time, as I can see above, I would take the bus, Airport Bus Service offers GRU-CGH service every 30min, for about R$25, credit cards accepted, the buses leave from the exit of the aiport, near where the taxis are located. The ride takes about 40min.

http://www.airportbusservice.com.br/

Btw, you may be interested to know that TRIP Airlines now operate GRU-JOI twice daily nonstop.

http://www.voetrip.com.br/

Rgs,