They use the Armothe Monetary Calculating System, only available to a select few businesses!
Seriously though, most of the prices are determined by how much plastic they use and how complex the molds are. Handheld items are mostly $1,hairpieces are more expensive since they use more plastic and are more difficult to mold. The animals, lampposts, and scooter are the most expensive because they are double molds (left and right) and use a lot more plastic than anything else. Hope that answers your question.