I'm going to be travelling through central/eastern europe for 3 months from mid may - late august.
The countries I'm planning to visit are; Czech Republic, Hungary, Slovenia, Croatia, Bosnia & Herzegovia, Serbia, Bulgaria and Romania.
How much should I budget per day for these countries? I plan to travel by coach or train, having heard that the costs for this type of travel is low in this region.
I would budget around 40 EUR per day for these countries. For some things prices are equal to those of Western Europe. This is especially true in the touristy areas. The exact cost would thus depend upon where you intend to go to in these countries.
Hostel beds are between 10-18 EUR in Eastern Europe, food from the supermarket costs about the same, eating out is a bit cheaper than in Western Europe.
Well T_maia is right on as usual. It depends where in these countries you go. Serbian is really cheap, even in belgrade.
Croatia is exoesnive on the coast - well, for east euro prices. Its def comparable to wstern Europe. Same as Slovenia, its on the Euro anyway. Prague is not gna be that cheap and similar in prices to Berlin. Budapest not too bad, more expensive than Belgrade but similar to Prague in price. Bulgaria and Romania are still very cheap. Especially in the smaller towns.
I would say 50 euros a day is very comfortable. Travel is cheap, trains or bus - they are about the same prices.
Hostels - 20 euros on average in large cities, small towns 12-15.