Question : What price range should you expect when booking from Tallinn (TLL) to Belgrade (BEG)?
Answer : Ranging from $303 to $318, prices for TLL to BEG fluctuate much less than most routes from Estonia. However, the sooner you book, the better price you tend to get.
Question : How long do most people visit Belgrade?
Answer : Of course you're not most people, but if you were, you'd stay roughly one day.
Question : Is price more important than specific travel days for you?
Answer : The cheapest day to fly in March is Friday. Flexibility is paramount when booking travel plans in order to keep travel costs down.