Watch out for 'GRID Car Rentals' and 'GOLD Car Rentals,' both tried to rip me off months after I returned home.
We rented in Cumbuco from companies in Fortaleza (which is a very nice city and I recommend you do spend some time there).
We payed 37$R a day for a 4 door sedan and hatchback (monthly rate). Shop around, you can get good deals.
I wouldn;t bother with buggies, they are slow, loud, cant lock your stuff in them, use lots of gas, and aren't very reliable.
Cheers,
Dan