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.
Not by much, the enclosure in the picture of the SVS sub looks to be 20" tall if if had to guess. A CapS1 is only 21" tall. I'd be willing to bet the overall size of the SVS sub would be very close to the size of a Cap S1 if it had gone into production.
Of course there's no point in worrying about though since it was never built.
This already exists, it's called the Captivator S1 from JTR but it comes with a 2400watt amp
I really want to get my hands on one of those. Every time Jeff and I talk about a unit for review he invariably leads the conversation to the Cap1000 instead. He's going to build me a Cap1000 and send it next month, but one of these days I want to hear the S1.
If you take yourself too seriously, expect me to do the exact opposite