ThinkGeek offers the Star Trek Men's Bath Robe in Gold (Captain Kirk), Blue (Mr. Spock), or Red (Scotty) for $35.99 plus $7.84 shipping. That's the lowest total price we could find by $19. It is one sizes fits all.
Think Geek also offers the Star Trek Women's Bath Robe in Red (Lt. Uhura) for $29.99 plus $7.84 shipping. It is one size fits all as well, albeit smaller than the men's version.