The test fee should be right at $150, though some test centers charge a few extra dollars for administrative purposes.
You can locate your nearest test center and book your appointment here: http://candidate.catstest.com/sitesearch.php
If you’re taking the test for the first time, the official name of the test is the “Unmanned Aircraft General – Small” test. If you’re taking the recurrent exam, you’ll see the word “Recurrent” in there.
The test fee is paid directly to the test center, not to Drone Pilot Ground School or to the FAA.