| Year | Average price |
| 1994 | 1.077833 |
| 1995 | 1.156667 |
| 1996 | 1.2445 |
| 1997 | 1.245 |
| 1998 | 1.155583 |
| 1999 | 1.175167 |
| 2000 | 1.525333 |
| 2001 | 1.466167 |
| 2002 | 1.381833 |
| 2003 | 1.601083 |
| 2004 | 1.857917 |
| 2005 | 2.312167 |
| 2006 | 2.615083 |
| 2007 | 2.8455 |
| 2008 | 3.305083 |
| 2009 | 2.396667 |
| 2010 | 2.833583 |
| 2011 | 3.576417 |
| 2012 | 3.686167 |
| 2013 | 3.576417 |
| 2014 | 3.358667 |
| 2015 | 2.517167 |
| 2016 | 2.2525 |
| 2017 | 2.530333 |
| 2018 | 2.817333 |
| 2019 | 2.68575 |
| 2020 | 2.25975 |
| 2021 | 3.09125 |
| 2022 | 4.4436 |