How much is ketamine treatment in USA for a visitor? I can't pay much. In Australia it's $150 per injection. I can afford much less say $50.

Depends. Ketamine can only be prescribed by a doctor and it requires a special license to write for it. Ketamine treatments cost usually hundreds of dollars in USA (from 400$ to 1500$/treatment). There is no standard price!
No standard cost... In the US there are no standard prices for procedures. Ketamine injections are not a routine treatment here so it may be difficult to even find a doctor who offers this. If you do, you would need to call the doctor's office to ask but any doctor would need to first do an initial patient visit and it would undoubtedly cost much more than $50. Health care in the US tends to be rather pricey.