My advice would be to offer big bucks to entice someone who is going that way or some old retired TDR member with little or nothing to do to go haul it for you.
Your best bet might be to try to get lucky enough to find someone who lives in Laredo that happens to be in Dallas or planning to visit Dallas. He could do it cheapest of all. If he lives in Nuevo Laredo or farther south he might be very happy to haul your trailer for free and keep going right into MX without stopping.
Keep in mind, even someone who lives in or near Dallas will have to drive to Laredo, spend the night, and drive back to Dallas. He will incur fuel expenses, meals, a motel, and normal wear on his truck. Someone who doesn't live in the Dallas area would have to drive even farther.
Anyone who would haul it for you for less than $1/per mile, loaded and unloaded, would be providing charity.