While access to case law is in fact required unless the case has been sealed by a judge, convenient and free access is not required. The states can charge for paper copies and make those copies only accessible via a USPS mailed form. That's the underlying problem. Barriers to access can be an effective tool for creating "expert" silos, where only those who have the means and the correct keys may travel.

Any idea of what the cost to, say, buy up all the case laws would be? And what is the law on republishing said copies?

Most docs are available through Pacer. Pacer pricing is $0.10 per page capped at $3 per document. Buying everything would cost a lot. In addition, new case law is continuously being created. So you couldn't buy everything and be done with it.

You can republish... court docs are in the public domain. RPXCorp tried doing this with patent law. For a time, they made everything free. That practice didn't last and they now pass on their costs to customers.

Just as it is entirely reasonable not to trust the state to do so either competently or altruistically.