If you are planning a return trip in the near future or a car transport in the opposite direction of a route you have previously shipped on, do not expect the same cost to ship.
There are many variables that factor into the cost of shipping a car. Route and mileage are important but are not the only factors. It is definitely not as easy as just calculating the cost per mile to ship a car. In most cases, opposite directions on the exact same route have different rates due to supply and demand. There is typically more freight per available truck being shipped in one direction or the other. This difference will cause the market to be higher or lower depending on which direction you are shipping.
That means that if your shipment is exactly the same as a previous car shipment except it is shipping in the opposite direction, it will probably not be the same cost to ship. Depending on your specific routes and the time of year it may cost more or less than your previous shipment.