Is there any reasonable cost-effective way to import these into the USA? Or is that path blocked due to regulatory safety things?

No, between safety and emissions, a normal person effectively have to wait out the 25 year as spelled out in the Imported Vehicle Safety Compliance Act of 1988. Once you hit that, it's relatively straightforward to import the car (straightforward if you know how to do it, there are importers who specialize in this market).

There are some small exceptions for show cars (as is, never used on public roads) and similar things, but they all limit/prohibit use on public roads.

1. Buy a BYD in Mexico.

2. Buy a scrapped Tesla in the US.

3. Rebadge the BYD with the Tesla's logos.

4. Bury the Tesla in your yard.

5. Register the rebadged BYD with the Tesla's VIN, slap some plates on it, and drive.

there are limitations, a non resident can get a car in for a year, and if it’s plated in Mexico a resident might get a similar permit.

register it with mexican plates and drive it over