The back of the card gives a value of $1 to the baseball that you would get for sending in a complete set. I used the inflation calculator at the link below to see that $1 in 1933 corresponds to $16.66 in 2010 dollars. (You can't use 2011 in the calculator.) I guess I am a little surprised that they would be reluctant to give away prizes valued at such a small amount.... Even given the depression....
http://www.westegg.com/inflation/infl.cgi