Working in Ag in Iowa, we would hire lots of Texans to work. It was generally a rule that every family member drove a car back to TX. They sold them in TX to people who would take them over the border. There are strict rules about US purchased cars there, but our workers still made a good buck getting them to TX. Rust, dents, and matching paint didn't matter as long as it ran good.
While in Mexico for work, I saw TONS of cars with MN plates that were long expired. They were the cars I would see on I-35 being towed down over the years, apparently.
I once saw a late 60's Dodge Demon in Puerto Rico with NY plates. That didn't get driven there....