For first-class mail delivery from Colorado to Arizona, the cost is 49 cents for one first-class stamp as of July 2014. Any number of stamps adding up to 49 cents equals the first-class rate. Standard mail offers cheaper rates for a minimum of 200 pieces or 50 pounds of mail.
Stamps come in "Forever" denominations that retain their first-class value no matter when they are bought. Other stamps cost 21 cents and 34 cents for lower classes of mail and bulk mail. The simplest way to mail a letter from Colorado to Arizona is to get one "Forever" stamp. Otherwise, customers need a combination of fixed-value stamps that meets or exceeds the current first-class stamp price.