US Postal Rates Data Set
Cost for a first class letter at certain times

Date      	Cost
          	(in cents)
May 16, 1971	8
March 2, 1974	10
Dec 31, 1975	13
May 29, 1978	15
March 22, 1981	18
Nov. 1, 1981	20
Feb 17, 1985	22
April 3, 1988	25
Feb 3, 1991	29
Jan 1, 1995	32