YoyoJam probably sells them wholesale at about $8.50. YoyoExpert’s markup is guaranteed nowhere near 200%. Probably 115% - 120%. If they want to say so, that’s their business. Most companies settle under the 200% markup line as well, which means it probably costs more than $4 to make one.
Stores make percentages of their products, not set dollar amounts.
That $30 is ONE example. Some companies have more expensive machinists, or anodizers. That figure does not surprise me, but small companies markup more. Also, which company was it?