It used to cost 300 gold. It was changed to 3 gold in February (patch 3.01).
Trinity ForceShopkeeper~ help me combine Trinity Force!Always curious about how an item is crafted...PeekingIt's fair price! Buy at the other side if you're discontent with it!You're just nailing them together, why does it cost 300 gold!?WHAT ARE YOU SHOUTING FORRRR!!
References Chen Ping-Wei(陳平偉),a shouting motorcycle maintenance man in Taiwan.300 gold as payment, just wait a minute~
The price before patch 3.01 released.