I went through ketamine infusion treatments and I live in California. The cost was $400/infusion. But my insurance did pay a small amount for the hospital/nursing care that goes with setting up and monitoring someone while they are getting the 40 minute intravenous infusion and then recovery time.
There are human studies out there, the link below is one example. You can go to pubmed to find more studies too. But yes it's ridiculously expensive and our health care system is so messed up that the price can very greatly. It's disgusting that our health care system takes advantage of desperately ill people. It seems the response rate varies depending upon the source, anywhere from 60 -80%. But the problem can be the response is short lived. They're also working on an intranasal spray es-ketamine but its not approved yet.

Serum BDNF as a peripheral biomarker of treatment-resistant depression and the rapid antidepressant response: A comparison of ketamine and ECT. - PubMed - NCBI