I'm thinking the best middle finger to the United States would be to have a one time, no questions asked, minimally taxed legitimization of all the unlaundered drug money in Mexico to make up for economic damage that Trump's tax may do and cozy up with China similar to Brazil to replace and increase foreign investment in Mexican infrastructure and trade.
i think its more likely they would threaten to station other countries' nukes than start a program of their own. a counter tax will probably happen but i doubt it would be enough to force a reaction from the white house.