They come up on eBay from time to time. There was one that went off at the end of March for $28+shipping. I would say that $30-35 is about what you'd expect to pay for her on eBay.
The flitterheart unipeg prototype is no longer offered by dealers on Taobao, she hasn't been for a while, so she won't come up as often as the blank flank rarity unipeg or the blossomforth unipeg.
Just keep your eyes open and you should be able to snatch one up.