Recent tripadvisor posts say that that cheap LAN domestic fares are point of sale, not residency based. In other words, if a foreigner can buy one, he is good to go. People can use Google Flights and click thru on a "residents' only" link to book a ticket. I have easily verified this. Haven't yet tried purchasing yet, but I will soon.
The tripadvisor thread says the purchase fails on entering credit card payment. The way to get around this is leave the DNS/Passport field blanks and/or use incognito mode on your browser. I'll report later if this works.