First, I’m going to offer a generic solution that I still think will solve your problem.
There are a couple of paid services, Flightfox and Darjeelin (there’s a referral link in my profile). You pay a small amount, set a price you want to beat, and their experts will find you something cheaper. If they can’t, you lose nothing (I’ve had them fail once and I got my money back). But they’ve also saved me tons. (disclaimer, I sometimes compete on their site as one of the experts).
Secondly, and this will actually address the issue with one-way flights in South America – it’s worth noting that it’s fairly common in South America to find return flights for far less than one-way flights. My friend, flying from La Paz (Bolivia) to Santiago de Chile was going to buy a one-way, then saw the price of a return was about half. So he bought the return and just didn’t use the second segment. So yes, you can do that. Check if it’s possible to cancel the return leg for a refund, although I suspect that’s unlikely – but at the least, it’s still cheaper than the one-way 😉
Credit:stackoverflow.com‘