From http://www.ageia.com/developers/index.htmlin why ageia?:

The AGEIA PhysX SDK is free for non-commercial use. Standard pricing for commercial use is $50,000/title/platform. Licensed developers who implement PhysX accelerator support in their PC title are not required to pay this fee.

That means we don't have to pay the fee unless we actually finish making a commercial game and start to sell it.