If you are in Ubud you do not necessarily have to book a tour for hiking. Indeed, there are several nice hiking tours around Ubud in the Canyons and Rice Terraces, which can easily be done on your own. One of those can be found, if you are at Central Market just walk westward on the Jalan Raya Ubud. At the Pura Gunung Lebah you head northward and follow the Campuhan Ridge Walk. You can see various fauna, lots of butterflies and nice views to the canyons.
Karsa Kafe is a nice stop for some refreshments.
I took this photo 2014 on my first visit to Ubud.

Campuhan Ridge Walk, Ubud, Bali, Indonesia
I hope you enjoy,
P.