I have read 'somewhere' that they only spawn on two shards. Europa and one other I can not think of. So unless you are on one of them shards, the cost of a Cu Sidhe plus a transfer is in the price. 300mio is a high price, but you want to be one of the elite right? If/when I find one that I can tame, I would sell for like 100 mio, but if people wanted to pay more, I think I could be talked into it.