Voting from Mexico

This is my first time voting in a US election from Mexico. I received our ballots and instructions this week and I am ready to return them to the US. For those that have done this before, what is the best shipping method to return the ballots to the US? Looks like DHL and FedEx are relatively expensive. Are there any other viable options from here?

Check your instructions on the ballot for voting from abroad. I'm able to fax my ballot to the Election Supervisor for the county where I'm registered in Florida.
https://vote.gov/voting-outside-of-us