It is worth the cost of the stamp.
In 2017, a Forever Stamp was worth 49 cents. This stamp allows the sender to mail a one-ounce letter regardless of future price increases, making it a convenient option for consumers. The price of Forever Stamps can change over time, but in 2017, it remained at that rate.
how much did a postage stamp cost in 2016
About $2.00
Most stamps will show the value of the stamp somewhere on the design.
a stamp in Montana costs 44cents
In 2017, the cost to mail a standard letter within the United States was 49 cents for a First-Class Mail stamp. This rate applied to letters weighing up to one ounce. Additional ounces would incur extra fees, with the price increasing by 21 cents for each additional ounce.
I have the stamp in good condition. It was for 15 cents.
Check your stamp at the link below.
44 cents per stamp
The E stamp had a picture of Earth on it. The face value of the stamp was 25 cents.
There isn't any stamp that is called a penny purple. You need to describe the stamp - include country and if you can date and what is on the stamp.
Without knowing which stamp, it's pretty much impossible to value.