There is a pretty good chart on the cost of neodymium (which the SB16 driver used) over here.
To sum it up though, the price of 1lb of Neo in June of 2009 (in USD): $5.68. In June 2011 it had skyrocketed to $114.02/lb (USD).
Several new entities have entered the arena, with mines in several countries coming on line that may drive the cost back down somewhat, and the trend has been showing that, but it is still very expensive to use. According to one analysis from Industrial Minerals, Nd sold in March '13 (reported in April) for $75-$80/kg, or $34.1-$36.4/lb (USD). Much better, but still over six times the cost from a few years ago.Edited by Snowmanick - 5/2/13 at 11:24am