Me and my girlfriend will be travelling in Eastern Europe for a month over the summer, I've been checking various threads about the benefits of inter-rail passes and it sounds like where the balkans etc. are concerned, the passes are not worth it. We want to be able to spend more than a few days in each country instead of trying to visit as many countries as possible and not have the time to learn much culturally. We're looking to cover Hungary, Slovenia, Croatia, Bosnia and possibly Serbia in our travels, although we still need to figure out an exact route.
My question is, are tickets going to be very expensive if we buy them as we go along, either on the day of travel or a few days before hand? Or is it best to have all our trains pre-booked before we leave? We'd like to be as flexible as possible, however, from my experience of travelling in Germany, train tickets have gone up by quite a lot when I've bought them on the day of travel. I've heard that travelling in Eastern Europe is usually much cheaper however.