The only thing that's paid is support, and the OpenJDK folks are Oracle employees (well, the ~90% of them who do ~95% of the work on OpenJDK). OpenJDK is an Oracle project in the same sense that Chromium is a Google project. In fact, OpenJDK (even more precisely - the OpenJDK JDK) is
the name given to Oracle's implementation of the Java SE specification, but we do get contributions from other companies, such as this particular great enhancement to JFR (even external contributions also involve significant work by Oracle employees).
Anyway, if you don't want to buy a support service, either from Oracle or any of the other companies that sell it, the use of the JDK is free. There is no "enterprise" flavour of the JDK, paid features, or use restrictions as there used to be under Sun's management. Java is obviously freer now - as in beer or in speech - than it was 20 years ago.