How to sell on Ebay

From México?

If your target buyers are in the US, you may find yourself at a competitive disadvantage due to shipping costs you will incur between here and there.

Would also depend on what you are selling--if MXN sourced items, there are tons of those on eBay from sellers who walk or drive them across the border into AZ, CA, TX.  They will ship domestically within US, at far lower costs than from MX.

I have a beanie baby for sale.

Take it to the local outlets of FedEx, DHL and UPS and let them tell you exact cost to ship to US (pick a couple of zip codes as they ask). I don't know if there is a local outlet for Estafeta.

Also it won't cost you anything to list on local FB page, Beg, Barter, Buy, Sell.  Lots of snowbirds here now; one may want to take it back with them???
https://www.facebook.com/groups/785666514831385/about/

It’s a rare item.

Back when there was a lot of back and forth travel, I sold things on ebay. I would time the sale to when my 'mule' was going and note in my posting that the item would ship from 'X' on 'Y' date. It worked well for small items.