The cost of hair extensions can vary widely depending on several factors such as the type of hair extension (e.g. clip-in, tape-in, sew-in, etc.), the quality of the hair being used (synthetic or human hair), the length of the hair extensions, and the location of the salon where you get them installed. On average, hair extensions can cost anywhere from $100 to $2000 or more. It is recommended to consult with a hairstylist or salon to get a more accurate estimate based on your specific needs and preferences.