Oracle's JavaSE implementation (JRE and JDK) is free of charge and this also now applies to JRockit.
While free is good, Oracle is also working hard on giving you reasons to pay for Java should you want to use some advanced features such as deterministic GC or advanced monitoring.
Both of these new products offer additional features (mostly from JRockit for the time being) but also disabled auto-update and usage tracking, both useful for massive deployments. This page has the licensing and install details and you can find pricing in the current price list (simply search for "Java"). There is also a FAQ available.
These new offerings essentially replaces Sun's former "Java for Business" and provide support for Java SE 1.4.2, 5.0 and 6.0.