I am not sure your statement here is accurate;
So a new gray market 500SEC in '84 cost $40,000 from Germany, and you add another $10,000 to get it legal and on US streets = $50,000.
I bought my 280SE, the original previous owner said he purchased the car in DM for the equivalent of about $13,000 from a German showroom floor in 1984. He said federalization was around $5,000 but he may have been assisted by the US Army for whom he worked at the time. Maybe it was around 40,000DM.