The following is information from Deb Will's WDW site:
The Harmony Barber Shop is located on the left as you enter the Magic Kingdom, past City Hall, tucked in between the "car barn" and the Emporium.
Hours are 9am to 5pm, seven days a week.
Cost for a haircut is $15.00 for adults and $12.00 for children. Pixie Dust, no charge.