Direct3D 10 will launch together with Windows Vista.
The price for Direct3D 10 hardware should be the same as for new graphic cards in the past.
From everything I have heard so far (talked with Richard Huddy lately) the hardware vendors will not wait for vista. This makes it highly believable that they want to sell the next generation for the holiday season.
Anyway the first D3D10 hardware generation is primary their fastest D3D9 (SM3) hardware with D3D10 support.