As the tours are hugely overpriced, take a break, take a local bus to TOCONAO, and stroll down into the beautiful oasis of the valle the jerez.
it is lovely lush and an altogether enchanting place,
take some sanwiches, and plenty of water, and dont forget the sunblock... you can easily spend all day there.
The bus leaves SP early, and around noon, and to get back be in the Toconao square at 16ººh. (Dont rely on that, it might of course all change, ask the locals!)