I would recommend packaging the item securely and take it with you to the airport when you leave. Pay the airline that you are traveling with the extra fee to check an extra item. You can check each carrier's website for fees associated with checked baggage and fees that you will be charged if the item is excessive weight. Be aware that any way you package your item, it may be opened through Customs and Border Patrol agents.
There are always expats making the drive back to the United States. You can always post on a talk group such as "Talk Baja" or "Baja Nomads" on Facebook to see if anyone can take your item.
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