No, Amazon does not have Project Natal for sale yet nor is there any indication on pricing. I think we can expect that news this week during the E3 Expo which the Microsoft Xbox Team is at in force.
However, Amazon has a product page up about Project Natal and they are now allowing you to sign up for an e-mail notification when Project Natal is available there.
Just head to the Project Natal product page at Amazon.com and look over on the right hand side for this:
After your signed up it is just a matter of waiting.
So do you plan to buy Project Natal when it comes out?