It'll be available to download some time today free of charge. But to actually create and edit documents you need an Office 365 sub which will run you circa $165\yr in NZ. The viable alternative I've been using for the last 2 years is Documents to Go Premium and Dropbox. Total investment was circa $29 with no ongoing fees.
I would have paid for Office for iPad, but a) not $165 every year ongoing, and b) with the cloud provider of my choice. Huge opportunity missed imo.