Couldn't find any nice one-piece example on Thingiverse so...
Designed and modelled this.
Print with low infill - to keep the weight down!
Printed with PLA 3 walls @ 20% infill = 29g – similar weight to Carbon fibre!
No rafts or supports needed.
Enjoy!

UPDATE: 10 July 2015
I've removed the original version and updated with a v2.
This one is stronger at the base and i've also removed the centre area. Print with high infill.

UPDATE: 2 June 2016 Created a v3 version with a thicker/stronger profile - print with high infill. V2 is still valid if your printer/material layer bonding is set up correctly.