> In .NET and Java it costs at least 100x as much time to throw an exceptions as to return an error code.

Don't know about .NET but in Java it is not throwing exceptions that is heavy but filling in stack trace during construction of a Throwable. It can be made much more performant using constructor that disables stack trace: https://docs.oracle.com/en/java/javase/21/docs/api/java.base...