A good way to see Rio, is on foot or by one of the many and very reasonable buses. Look for the AC ones -- only marginally more 'expensive' than the ones without. Best part, they all have a fare collector inside, besides the driver. Very civilized and they will not only make change but also tell you when to get off, if you ask them nicely. Best thing next to the Hong Kong "Octopus card"!

For "tours", use a cab! We had great experiences and saw most of the things we normally would have booked a tour for, this way. Find a cab, negotiate the destination, waiting time there and return trip, agree on a price and pay at the end. We even toured Corcovado this way, were allowed over an hour up top and all for much less than tours arranged by the hotel or other source. Best part, you leave when YOU want, not on someone else's schedule. And no side trip to purchase something, unless you want to.