My 2 cents' worth:
Thirty to forty years ago, getting a Southern car was a much bigger deal than it is today. Back then, one main reason for buying a new car every 3-4 years was that the bodies rusted through so fast in states using salt in the winter. The more modern cars can remain nearly rust free far longer now if you do some basic cleaning year-round. So, the difference in price in the same car used from Ohio and from Georgia used to make it well worth it to transport the cars here. Today, it seems that how the car was maintained makes a much bigger difference in prices compared to what state it was used in.
I'm not saying that I want to buy some rusty old car, just saying that where the car was kept for its first 5 years doesn't make quite as big a difference in price today as it did when your dad was younger.
Buying a 1940's through 70's car? Makes a huge difference if it's been in Arizona and not Minnesota. Also, with stretch limos (which tend to get rust in the coachbuilt parts), it still makes a big difference if it was used in the salt.
On the flip side, an older classic pickup truck is worth far more in the South than it is in Ohio. Just a lot more demand for them there.
With the widespread use of eBay Motors and similar online sales, the differential between the value of a vehicle from one region to another has lessened compared to what it was just a decade ago.