Thanks to inspiration from this thread I was able to get our flight to Patagonia ( SCL to PUQ) for next March with Avios. LATAM wanted $700 each ( although I did not try the Chilean site) and LAN km program ( which I joined in anticipation of this trip) won't allow a one-way booking. But Avios would. I would not have known about the Avios solution had I not read it here.