What airline are you looking at? If its not actually a resident only fare, then there is no problem using a peruvian IP to buy, such as with Peruvian Airlines which is often times the cheapest. If its Lan and you're using a peruvian IP, then those are resident only fares. I think the terms say they can charge you $180 more if they determine you're not a resident, but as long as you check in online and dont check a bag at the airport, you'll be fine (sometimes even if you had the pay the $180 fee it would still be cheaper). I've flown 8 or 10 resident only fares and never had a problem....printed my boarding pass at home and went straight to the gate.
You can also check availability with Avois, 9k RT.