Where three foreign students could get a cheap accommodation for the whole summer in ocean city?

Answer 1

Can you be more specific?
US? What state?

Ocean City, Maryland:
http://www.oceancity.org/
http://www.ococean.com/
http://travel.yahoo.com/p-travelguide-476450-ocean_city_vacations

Ocean City, New Jersey:
http://www.oceancity-nj.com/

Or try Hotels.com:
hotels.com/

Have a nice summer!