He is no match for the UAW.
Even if Musk could get a subsidized deal, as well as an initial deal to keep the unions out, even after signing a contract which prohibits unions, once these previously unionized employees are rehired, they will hold a vote, nullifying this portion of the contract, and put him out of business very quickly.
Forget any reprieve from the courts and Democrat Party which reside over all of these jurisdictions. They also depend on the UAW for their existence. They will always side with the unions and welfare minded workers. This is how they stay in power.
Musk cannot break this cabal up.
Michigan has been a Right-to-Work state since 2013. He could setup a no-union plant and probably pay the employees a rate comparable to the hires at GM and Ford. The last UAW contracts setup a two-tier pay system for long term employees vs new hires.