Where are these mythical cheap pilots coming from?
Europe, not likely. USA no way they are booming. SE Asia, no way. So what a few from South Africa and the odd European who wants a change of scenery?
Why would they be any cheaper than local guys, they would be employed on the same EBA. In fact they cost more to get on line due to the admin costs involved dealing with immigration.
The 457 (old name) threat is an empty threat.