No, getting a 100% equivalent working Java system is trivial. But the goal is having something that looks like it was Java from the start not Java as written by a cobol expert. So proper use of classes. Not al globals. Sensible naming etc. The real cost is in maintenance of the code: having in idiomatic Java could help. Translating to idiomatic Java is very hard
I think those companies would kiss you on the mouth and do any unspeakable acts you requested were you able to promise a 100% equivalent system in Java. There is a ton of industry experience in turning working-but-trash Java into something more maintainable.
