I don't think it is just BAT, the overall air cooled market has gotten crazy. Check out this FB ad:
https://www.facebook.com/marketplace/item/453160982246290/
I sadly believe these cars have become a commodity and too many speculators now look at these treasures no differently than AMZN or BRK.A stock.
"too much cheap money sloshing around the world" - Lou Mannheim