I think there is a lot of room to go with Willie Mays card values.
Many think he is not only the greatest living player, but the greatest player period. For example, the
Athletic (Behind a paywall), has Willie Mays #1 and Babe Ruth #2
Buster Olney (ESPN analyst) has said Willie Mays is the greatest player ever as well.
And yet, you can buy Willie's '51 Bowman rookie for just over half of what Mickey Mantle's costs. This is not a knock on Mickey Mantle, but they were both Centerfields, and Willie Mays was better at basically every facet of the sport, with the exception of maybe clutch hitting in the playoffs.
I think as far as investments in post-war go, Willie Mays is up there with the best going forward.