Go through your results for flights to Harlingen in the USA with Netflights. Although United Airlines usually has the best prices, it's best to double check what's available for your travel dates.
If you don’t have set dates for when you want to fly to Harlingen, try searching by month – that way, you can compare airfares throughout the year.
Look out for flights with United Airlines, as they often have good deals. Or broaden your search by looking at other airports in the USA.
You can also broaden your search by looking at more than one departure airport. Have a look around – you might be able to save by flying from a different airport or city.