well depending on the version you want, the price will be relevant.
i found this on the internet
Windows Vista Home Basic
200 euros or 255.55$ or 135.95 pounds
Windows Vista Home Premium
400 euros or 511.10$ or 271.90 pounds
Windows Vista Ultimate Edition
500 euros or 638.88$ or 339.87 pounds
Windows Vista Business
650 euros or 830.54$ or 441.84 pounds
Windows Vista Enterprise
800 euros or 1,022.20$ or 543.80 pounds