I work for a global organization, which is making car components all over the world. You'd be surprised, how similar the final costs of many components are, no matter if they are made in Europe, Mexico or the US.
In the countries with high labor costs, you see a lot more automatization, have lower logistic costs, less currency risks, qualified personal is usually easier to find, less capital is employed during the transport of the goods and so on.
For parts which can be produced in a highly automatized process, a few percent (often less than 5%) in import taxes or change of the exchange rate (e. g. if China would stop keeping their currency artificially low), can often make all the difference between a production location in China, Mexico or the US.
Just think about cars of which some models are made in the US, while others are made in Mexico - its not like the US made versions are 30% more expensive, as some want to make us believe. IF our new government is keeping what they promised, and will also lower the corporate taxes and provide other incentives for local manufacturers, the costs for many products might remain unchanged.
For stuff which cannot be made in the US, I would however indeed expect a price hike, depending on the tariffs they finally settle on. It will therefore certainly not be possible to bring all production back to the US.