On XBox One, my son plays Forza Horizon 2 and he's been finding free cars in the Auto Show. I cannot find any! How does the aspect of free cars work in Forza?
Maybe this are the barn finds. In FH2 there exist 10 cars that you can find on the country side and then are added for no costs.
Here you can find more information: Where are all the Barns located in Forza Horizon 2?
Sorry, but I can not comment yet. I will delete this answer if it does not help at all :)