I just got home from a Lorraine Lea linen party and they had a couple of different kinds - one was a fitted one with the skirts and elastic to slip over your whole mattress, with a built in 'comfy' padding, at about $119 each I think (don't quote me but roughly) OR they had just a waterproof liner that you laid on top but was meant to be mega absorbent, for I think $59?? Something like that. They have a 10 day return policy, but you only get a credit, no cash back if you don't like it.
Edited as I had a brain fart moment and now realise you're after a doona protector - they had those too but I didn't pay attention to sizes or prices, sorry smile
[Edited on 09/02/2010]