As you perused the forums, you may have noticed that our subject matter is entirely centered around wilderness hiking on backcountry trails, as opposed to low-cost international travel. It isn't entirely clear from your post, but were you thinking of tramping around Serbia's mountains on foot?

No matter. If someone here has traveled in Serbia they're likely to pipe up, but in the meantime you might want to check out the international travel forums at lonelyplanet.com. Good luck with your internship. I'm pretty sure you'll have a wonderful time. Stay healthy!