OG Can-Am was different - there were fewer rules, so things were limited by drivability. (Someday I hope to add a Can-Am car to my collection but I am also limited by driveability)
i have a '60s lotus 23, which was built for Le Mans, and it was very low six figures. but an engine rebuild is $30k...
Trackdays skew towards much more modern cars. Although I met the shop that takes care of my stuff at one (they did Spec Miata rental, and now I race that too)