Romania for sure... and the city of Iasi in north east of Romania, because is very populated with students, night clubs, restaurants opened 24/24. The prices are relative cheap, but if you want to rent an apartment there you need to know are like 300 euros / month. Is the city i actually live and study and i can tell you after Bucharest is the only city in Romania that never fall in sleep (maybe in summer when students are gone). Also many foreigners here (italians especially). You can have a lot of fun. Bellow are some informations.
http://en.wikipedia.org/wiki/Iasi
http://www.iasi.ro/
http://www.romaniatourism.com/iasi.html
http://www.iasicity.ro/