I agree with mul-ta, the issue can simply be where you are in the world. I see lots of NSS Wind Whistlers rather than SS Wind Whistlers. So keep an eye on European Ebays and you will get her at the best price.
Final price will vary mainly down to the colour of her hair and how faded or pink it is. However even with nice pink hair, as long as you watch on UK ebay, I would not expect to pay more than $10 for her.