BFG has a product on their site, but no model number(s):
Both Dell XPS and Alienware are already offering systems with the card for $250-$275. So while not cheap, its not a stupid price either. According to Ageia, you will not have to update the card as their driver is supposed to make it somehow future friendly.
From Ageia site FAQ:
Do I have to buy new hardware every year just to get new physics features?
No. The powerful, yet flexible, AGEIA PhysX processor is designed to enable future enhancements via software. This makes a PhysX accelerator a great investment because gamers will get not only new PhysX-enabled games now and in the future, but the new features that AGEIA delivers via regular driver updates will run on the hardware that’s installed in PCs today.
Is this a Fad or the Future?