I run PlainSite, which indexes about 10 million dockets and is mentioned in the OP's post. I have experience in this field.
PACER is of value not only to litigants, but also to journalists, academics, employers, and average citizens who are interested in any given topic, individual or company.
Litigants who need PACER access but can't afford it are almost never given free access. When you file on CM/ECF, the e-filing side of PACER, you are given one free bite at the apple for documents in your own case. Legal research involving other cases is not free. Second attempts to view documents in your own case are not free. In forma pauperis status does not make your access free. PACER waivers are not granted to anyone but select academics, and then, rarely.
Many opinions are not properly tagged as opinions since it is each individual judge's responsibility to handle the tagging. PACER charges for them anyway, even though they are supposed to be free. This applies to tens or hundreds of thousands of documents on the system. See https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3034399 and https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3026779.
It is rayiner's opinion that it's not unreasonable for the government to charge an access fee per page for PACER, but it is the law (the E-Government Act of 2002) that doing so is inappropriate and illegal. Recently, the authors of that Act, Darrell Issa and Joe Lieberman, filed an amicus brief explaining their position on that matter yet again in the ongoing litigation. See https://www.plainsite.org/dockets/download.html?id=246610557....
The marginal cost to the government of filing a new suit is substantial; hence the filing fee. The marginal cost of providing one more PDF to the public is zero. That's an important difference.