[Update; October 21, 2022 - The bulul realized 630,000 Euros (that's 36,000,000 pesos and some change) during the auction. This is more than double the maximum estimate of 300,000 Euros.]
The "bulul" is estimated to fetch between 200,000 to 300,000 Euros. That's between 11 to 17 million pesos. Why is it very expensive? There are a lot of factors that decide a work's auction price. These include source, age, material, condition, size, and provenance.
Provenance is very important in this case. Provenance is basically the "history of ownership" for the statue. Who owned it? How did it transfer from one owner to another?
This bulul came from the collection of William Gambuk Beyer. William is the son of no other than H. Otley Beyer, the American anthropologist who is often referred to as the Father of Philippine Anthropology. The bulul was then acquired from Beyer by Alain Schoffel in 1970. The Caput couple, in turn, acquired the bulul from Schoffel in 1989.
The accompanying essay for the piece states thus:
"A masterpiece of Ifugao art, this sculpture dazzles by the universality of its form. Thanks to its purified aspect, we can see as many possible links with the great statuary of the past as with that of the present. Notably, thanks to its intrinsic geometry, it is possible to evoke a kinship with some of the oldest anthropomorphic representations, such as certain plastic creations of the Neolithic or Cycladic art. At the same time, by reducing and simplifying the anthropomorphic representation as much as possible, the artist has created an abstract interpretation of the human figure, giving it a powerful serenity. In the case of this formidable sculpture, it is its great plastic quality and in particular its formal ambiguity - its archaism and its modernity - that convey an indisputable timelessness."