I have no idea what the going rate for CFIs is, but based on that pay, if you were doing 100 hours of work a month you'd make $4700. 100 hours doesn't seem too much considering it includes ground duties as well.
Not to mention, Bali is cheap.
Plus housing AND food allowance (or eat at their school with the students - 3 meals) your choice. I think it's reasonable. All expenses covered, so all your money is pocket money ... unless you have student loans like me! Either way...it's not bad...