how much would a hacker be fined for using others online money? (according to international law)
Let's say for using $10,000, $1,000, $100, or $10.
There are no international laws that govern all hacking around the world.
Generally however, criminal statutes require that the accused, if convicted, be ordered to pay restitution to their victim(s). This is generally for the actual financial amount required to restore the victim to their position, had the crime not occurred.
For your examples, it would be for the actual amount stolen, as well as any other costs involved such as legal fees, conduct money for court appearances or lost income that the victim would otherwise have earned for example when they were giving evidence, or possibly bank interest that the victim would have otherwise earned.
This is all in addition to any statutory or other sentence (fines, imprisonment), which vary around the world - if you want a specific answer, give a specific jurisdiction.