It is very much a fork in the road for you financially.
If you want to move ahead then an IR at the least opens the way to multi time if you were to get a charter job. Though more difficult to get.
An instructor job will see you stuck on single engine for quite some time and then you are going to have to shell out $ to progress to multi anyway...
Do a casual walk around to some of the charter outfits and have a talk before committing to either path, see what they say. Given your predicament to being tied to Melbourne, that could infact be your selling point for some of these charter companies as being a longer term employee.