That might be misinformed, although $2-6k per infusion is very very high. That price is simply providing a high profit to the provider

There is a group of doctors who provide ketamine therapy and they've created some resources for interested patients. They say cost should be $400-800 per infusion and outline the drivers: http://www.ketamineadvocacynetwork.org/cost/

Fwiw, $800 is the price I was quoted.

You're paying for the risk that the doctor is taking. It's going directly into his pocket though. That's why regional prices are so far apart.