It is, and its 100% funded by the fees they charge attorney's and others to access the documents. The amount of fees and use of them is somewhat ridiculous currently, but if they remove the fees without setting up an ongoing funding source I'm afraid it will stagnate like many state court systems.
Well, the fees aren't wonderful, but the information you can get out of it is excellent. I grew up in not-America, where access to court records is even more difficult and expensive (e.g. have to have a lawyer do it for you).
I didn't know that Free PACER was a thing, but I'm happy that it is!