According to the post office, it would be worth 8 cents. I think it would depend on how old the stamp is, but it could be worth more to collectors. If it very rare, it could be worth a large amount of money.
an 8 cent stamp is worth 8 cents - unless it is a stamp of historical value, has a unique postmark and or is printed with errors - but usually a 8 cent staff is worth 8 cents. Collectors will pay more for the 8 cent staff if it is unique. The PO values it a 8 cents.