http://www.net54baseball.com/showthr...ighlight=group
Basically there were a couple of people (5 according to the owner of PWCC in an article) who were buying up a group of post-war rookie cards to influence the market. Mainly 1952 Mantle, 1954 Aaron, 1955 Clemente, 1955 Koufax, 1963 Pete Rose. Prices increased 300%-500% for the cards in the same grades in a span of a few months.
One more recommendation when using PSA's auction prices tool, make sure the prices you're seeing are for the correct card and not a complete set headlined by that card. If the card is part of a group, they will remove that price point from their database if you click the "report this item" button.