"International rating" as in the combination of your prestige, industrial rating and military score compared to others? That's not it, it's the prestige alone. Negative prestige equals no diplomacy. Industrial rating and military score don't enter into it.
It doesn't cost anything to open negotiations; some actions will cost money if you go through with them, but you won't be barred from all if you're broke.
It doesn't cost anything to open negotiations; some actions will cost money if you go through with them, but you won't be barred from all if you're broke.