While the phrase "price for something" is not ungrammatical, it occurs in English by far more seldom than "price of something" (for the same "something"). You can look those up in Google's ngram viewer. I did, with "price of/for bread", "price of/for grain", "price of/for gold".
The reason for that is, I believe, that the preposition "for" creates some distance between the concepts, as if "price" is somehow independent from the product and is said to accompany it or to serve it.
Generally, however, we perceive the price as one of the characteristics that belong to the product, not unlike color or production volume. That is why we more likely say/write
How are the falling global prices of natural resources impacting the United States?