You're looking at $5-12 a piece depending on whose selling, what condition and where you get them! Ebay seems to have them pop up quite often, but a lot of the times you can find them here. They are quite common, and sometimes hard to sell which means sellers start their prices off on the lower side and sometimes even reduce their price. (I know I had a ff cotton candy sitting in my sake box for over a year.) the exception is really mint ones which can fetch 12$+
Hope this helps!