Obtaining APEX
APEX is distributed (actually embedded) in Oracle XE and Oracle 11g. In both cases, the embedded version is not the latest, but it can be upgraded to it.
The latest version of APEX, as a standalone tool, can be downloaded from the APEX home page on http://www.oracle.com/technology/products/database/application_express/ .
You can use APEX, free of charge, as long as you are using it on a valid licensed Oracle database (starting with 9.2.0.3), Oracle XE, or under the development terms of OTN.