Details on the Pro variety of Microsoft’s Surface tablet have been hard to come by since the company first announced it, but it’s filled in some big ones today. It’s confirmed in a blog post that the device will start at $899 for the 64GB model, with the 128GB model setting you back $999. Both of those are what’s Microsoft’s dubbing the “standalone” model, which means you’ll get a Surface pen/stylus, but have to shell out extra for a Touch or Typ…