My youngest brother and his friends rented a prom house down the jersey shore.  Apparently the guy that owns the house is a genius.  He bought a big old house, and rents it out to proms every year.  He hires 2 security guards, one at the door and one in the house.  He doesn't care how many kids stay at the house but there needs to be a firm number and the kids get wristbands.  He charges around $400 per kid.  Parents love it because they know the parties wont get too out of hand so they happily pay, kids love it cause they know they can't get in trouble.  Just from my brothers group the guy had over 30 kids in the house over the weekend.  That's $12,000! apparently he rents the house 6 weekends in a row to different schools during the OFF SEASON!..  He then has the house to rent all summer long during peak summer rental probably around $4,000 a week for 12 weeks.  My brother's school has had a group of kids rent this house every year for 6 years running.

So by my calculations this guy is bringing in around $120,000 a year on this property.  Of course there will be fees for security guards, but there wouldn't be much damage as the security guards would be there regulating.  So figure even if the house has a $3,000 mortgage and after he pays the security guards he is still probably cash flow positive $80,000 a year on one property!