You will need the WebDev 12 App Server to deploy dynamic WebDev 12 sites. WebDev 12 sites are not compatible with the v11 App Server. However, WebDev 11 sites will run under the v12 App Server.
The price is EUR299, as listed in the price list. The US deployment version is not available yet, however a free 10 connection version comes with WebDev 12, which will be adequate for a lot of people.
-Peter