Hello David and all,
This is in regard to Lignum vitae (Guiacum officinale and G. sanctum) and its substitutes, especially Bulnesia sarmientoi and B. arborea. I couldn't walk into a shop and know the difference--would have to ask the vendor. I was suggesting that differences in price can sometimes be explained by differences in the article being sold.
Here is a vendor who sells both Guiacum and Bulnesia, and discusses both a bit:
http://www.exoticwood.biz/lignumvitae.htm
If you follow his links to Argentine lignum vitae, B. sarmientoi, he says that it is a bit lighter in color than true Guiacum, and is the best of the substitutes. He also says that Guiacum is very rare these days in trade.
Here is a link which discusses Argentine lignum vitae, or Palosanto, and its uses. Note its density which is in the same ballpark as Guaicum:
http://en.wikipedia.org/wiki/Bulnesia_sarmientoi
In the above and elsewhere, I found 5 or 6 different spellings of Guiacum--and used the one most seen in dictionaries.
Wiley