Window air conditioners cost about $120 at the low end (for 5000 BTU) and consume about 500 W of power. At 35cents/kwh, that's 17 cents/hour. Not too horrible.
First they are more expensive to buy over here (and thus also beyond my financial capabilities)
Second they are less practical over here as we have casement windows (had to look this term up
)
According to the landlord the neighbours in question stated they have sent a termination of contract yesterday, so that should fix it in the long run- if they spoke the truth, that is
The bottle thing, while being fun, would just create more of a mess I'm afraid. If they don't care for all the filth , garbage and feces now, they won't do after as well