In Frobane Inc., a battery manufacturing company, the inventory on January 1st 2018 was valued at $4,500. Additional raw materials worth $5,000 were purchased through the year. The cost of labor was $10,000, and miscellaneous costs amounted to $780. The value of the inventory at the end of 2018 was $7,500. Frobane had no finished goods inventory at the beginning or end of the year. 

Calculate the cost of goods sold by Frobane in 2018.