In the current award data, only United Airlines shows nonstop space on Houston–Santiago, but as a Star Alliance member its seats also price through alliance partners, not just United MileagePlus. If you're open to a stop, the better-priced connecting awards in the data run through Toronto, Miami, and Dallas/Fort Worth. In economy, the floor sits on United Airlines but books through Virgin Australia Velocity, a partner redemption. Only five airlines show award inventory on the route, so date flexibility matters more than carrier choice.