You have asked for minimum development work so ... "Write your email address legibly on a piece of paper and mail it with a US $1 bill to $ADDRESS." Obviously

You have asked for minimum development work so ... "Write your email address legibly on a piece of paper and mail it with a US $1 bill to $ADDRESS." Obviously 1) it will cost people 68¢ for a stamp, 2) won't really work for people outside the USA and 3) if you only sell fifty copies it's not a wildly silly suggestion.