Hi Guys. The reality is that I have many drivers that have been sold for years and just lacked time to get them on the website. The SBP series are just one of those examples. They have been made since back in 2001 by Lambda and we have been making them since 2005 or so. The motor design gives flexibility to use coils with either flat copper, flat aluminum, or round copper wire to get different parameters. Lambda had many different drivers using different combinations of parts which you can see on the archive site. All of them are drivers we can still make today.
Pricing on the SBP drivers can be found here from the May updated pricing:
The SBP series are basically mass loaded TDS woofers with dustcaps instead of phase plugs. They use the same coils and cones but have added mass to raise the Q and push the Fs a little lower. They have a more limited bandwidth than the TD woofers due to the dustcaps. They are recommended for a maximum Xover frequency of 500hz. Typically when going over 250Hz I would suggest a TDS vs an SBP woofer.
The SBP15's have been used in many recording studios to provide the bottom octaves. We had a designer in the UK using them for the low end in many of their studio installations. Several hi end speaker systems like the Evolution Acoustics MM3 and MM7 use a slightly modified SBP15. As mentioned, the SBP12 does bear some resemblance to the Seaton drivers. While they do share some common components there have been other modifications done to optimize the Seaton drivers specifically for the Catalyst application as Mark mentioned.
Recently they have been gaining more exposure as infinite baffle woofers in automotive applications. Larry Woolacott won the IASCA Ultimate World Championship in 2012. He also won the Triple Crown for SQ + RTA + SPL and actually had the highest score in history at the time. http://www.aespeakers.com/news.php?start=5&news_id=28