I made reservations with Zen Tours, one of many touroperators in the town. In my opinion, these people were the most friendly, and the tours they offered are more or less the cheapest in town. And I can assure you, in general the tours are very expensive!
Keep in mind that the guides don't speak any english, which is a pitty! If you want a english guide for one day, you can easily pay 100 reals!!!!
So I was glad the tour I made wasn't only informative, but also verrrrry active. And we saw a lot of the region just in one day.
I payed 35 reals for a tour of 1 day.