Windows 10 Home has been listed for $119.99 and Windows 10 Pro is for $199.
On listing page, it was showing shipment date August 30. I am not sure why the date is set to August while the launch is scheduled for July 29 and will be available in phases.
If you are interesting in buying Windwos 10, you can pre-order now and book your copy.
Pre-order links: