Hm... I see, I found another formula, but a little difficult to calculate.
You must to know what the products you need to make a Goblin Halberd.

Goblin Halberd <- Skeleton Iron Sword R19 + Vertical Wing R21
Skeleton Iron Sword <- Iron Net Boots R17 + Wolf Tooth R20 + Iron Net Boots R17

Iron Net Boots can be bought in Cairo, Egypt with price of 610 golds.
Wolf Tooth can be obtained from Snow Wolfs in South Pole.
Vertical Wing can be made from Bench Saw and 2 Oak Woods in 6 minutes.

2x Iron Net Boots + travel expanse = 610*2 + 1200 = 2420 golds
Wolf Tooth + travel expanse = 1000 + 600 = 1600 golds
Vertical Wing = 30*2 + 6*100 = 660 golds

2420+1600+660 = 4680 for materials.
2x compound to Goblin Halberd: 4680 * 2 = 9360
For failrate risk guarantee, often doubled = 9360 x 2 = 18720 golds.

So the price of Goblin Halberd is 18720 golds with the range price: 17k-20k golds.