By the end of 2006, the cost had doubled to approximately $320 per ton, and then it almost doubled again in 2012 to approximately $610 per ton.
baɪ ðɪ ˈɛnd ʌv tˈuː θˈaʊzənd sˈɪks, ðə kˈɔst hæd dˈʌbəld tʊ ɐpɹˈɑːksɪmətli dˈɑːlɚ θɹˈiːhˈʌndɹɪd twˈɛnti pɜː tˈʌn, ænd ðˈɛn ɪɾ ˈɔːlmoʊst dˈʌbəld ɐɡˈɛn ɪn tˈuː θˈaʊzənd twˈɛlv tʊ ɐpɹˈɑːksɪmətli dˈɑːlɚ sˈɪkshˈʌndɹɪd tˈɛn pɜː tˈʌn.