Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Harlingen, Texas to Guadalajara as you normally would.
HRL and GDL are unique codes to identify airports used in the aviation industry. They are defined by IATA (International Air Transport Association) and are commonly called IATA codes. HRL to GDL refers to a flight route from Harlingen Valley Intl Airport to Guadalajara Miguel Hidal Airport.