there are a few suppliers of them, but where ever you go it will be about the same price.
they often come up on e bay for a good price if you dont mind a second hand one. and i think thats about the only place to get one for under the rrp.
where ever you buy one from, even if you do pay full price[which does seem like a lot at the time] i dont think you will regret your purchase. they really do make a world of difference to your technique when you are just starting out.