A lot of these cards we are talking about may have "booked" for very little money many many years ago, however, finding one of them back then was basically impossible. Ruth Baltimore News California League OJ's etc. all fall into this category. The Ruth basically was not known to exist and the Cali OJ's while booking for little--good luck finding any (even then) for those prices. I will second the 1911 Halla spoken of earlier. I picked mine up maybe 5 years ago for roughly $30, and a few years earlier it would have been roughly $10, finding one today would set you back maybe $1500-2000 for a decent one--although I haven't seen a straight sale of that card individually in the last 3 years, there was the 19th Century auction w/ a SGC 20 (I think) Halla w/ 3 others that sold for $2000+ (granted one of the others was also a known rarity)
Price increase from $10 to roughly $1500-2000 is 150-200X the price in ~6-10 years
-Rhett
Edited to add: It was an SGC 20 (although it looked a bit undergraded-it looked like a SGC 30-40 to these eyes) w/ French, Fitzgerald, and Fullerton for $2,300.