The average auto worker in the US is paid $38 per hour.
The average auto worker in Mexico is paid $9 per hour.
Even high level veteran machinists and specialists at the Ford and Ram plants in Mexico only make about $20. It's a big deal that the new Mercedes factory in Aguascalients is going to be paying their senior line techs the equivalent of $24 right now. German Merc plant workers make about $60 per hour.
Due to costs of living in Mexico though, Mexican workers still make a decent money in relative terms.
Germans build some performance models in Mexico but not many. The next generation G20 3 series will be built in Mexico for the entire North America market. BMW hasn't decided if it will build the next gen 5 or 4 series there, but it's very likely that it will be the 5 as that segment has become much more competitive as of late.
A big reason why American manufacturers can continue to provide such bang for the buck compared to the Europeans is utilization of cheap Mexican labor and supply chains. Were every component on performance GM, Dodge and Ford vehicles produced in the US with higher labor, you could expect a 20%-30% increase in MSRP, thus greatly diminishing the cost advantage that US marques have over the Europeans.
Japanese and Korean brands manage to provide bang for the buck by utilizing massive integrated supply networks and more automated lines than the Euros do.
Eventually Mexican labor will get more expensive and American manufacturers will either have to up the price of their vehicles or create more efficient, automated assembly processes.