Serbia remains a contry with low cost of living, specially for those who come from Western or Central Europe, and US, Canada or Australia. Daily budget of 40-50 Euros is more than enough fully enjoy your stay in Belgrade.
Main course in restaurants: 8€
Cigarettes: 1,60€ pack
Beer: 1,80€ pint
Taxi: 5€ (10 minutes ride)
Renting an apartment: 300€ month
Short term rental for a few days : 40 à 70€ night
Hotel room: 80 à 120€ night