On checking your NBN service is a FTTP (Fibre to the premise) , as such it is difficult and expensive to relocate the NBN core equipment.
However from experience it will most probably be more cost effective to use a Power Over Ethernet WiFi Extender (as long as all power points feed off a common Power distribution board ) to extend WiFi coverage to the area you need it.
We don't have any lists of the best WiFi extender for you to use, but you may check this discussion as it will provide you with some insights from the end users.
You may also check the WiFi Mesh system which is quite a trend right now. You may check this forum link for more information.