Actually that changed for Perú. In Dec 2017 LATAM stopped charging the resident prices, and in February 2018, also did Avianca. Those were the only 2 Peruvian airlines that had a different price based on your residency status. It changed bc most local airlines –unlike LA and AV, which are international holdings– did not charge it and they had started winning a larger quota of the tourist share.
So buy off whatever you want, they won't try to asses a fine for being a foreigner.
Sources:
LATAM, Avianca