B Burini stands for Ballone Burini - the manufacturer of your accordian - located in Castelfidardo - a town and commune in the province of Ancona, in the Marche region of central-eastern Italy - started in 1920.
Unfortunately we cannot give you a value - one would have to be determined by a knowledgeable person who has to visually inspect as well as play it to make sure it is in proper working order. (We have an accordian player in the family - from the days of Lawrence Welk and his orchestra).
Contact your local music store to see if they can help you or refer you to someone that can help you.
In the meantime here is the English version of the website for Burini
www.balloneburini.com/home.php?Lan=En
