The prices for the virtual machines with the Oracle license included run from about USD 820 per month for Oracle Standard Edition (SE) running on 2 cores, to a whopping USD 9300 per month for Oracle Enterprise Edition (EE) running on 8 cores. These prices are for Oracle software only and do not include the cost of the VM, which is billed separately.
Alternatively, with "License Mobility", you obtain a license as normal from Oracle and run that software on Windows Azure by deploying a Windows Server or Linux VM and installing a copy of the licensed Oracle software. Azure is listed as an "Authorized Cloud Environment" in the Oracle Cloud Licensing Policy. As I understand it, this policy allows you to use Oracle Standard Edition One (SE1) on Azure (up to 4 cores = 1 processor license, up to 8 cores = 2 processor licenses), which would be a quite cheap entry-level option for small businesses, since you would pay once for a perpetual database license, and then just pay monthly for the Azure VM (ie just the Windows/Linux Server software, not the database).
There's also an article at ZDNet with more details.
