I have been taking the trains through Bulgaria and Romania and it has been interesting at times. Sometimes the bathrooms don't work, sometimes the doors won't close. But, the prices are definitely right and has been very helpful with my budget! Taking the trains from Sofia to Plovdiv to Veliko Tarnovo to Bucharest cost a total of about $30. And, at times, had some great scenery.
The best part is the people I have met along the way. The nice gentleman from Ruse, Bulgaria that helped me find the correct platform 3 in Plovdiv...yes there were two of them; the German couple traveling around SE Europe instead of going to school this semester, the Moroccan and Egyptian girls that gave me great travel ideas, etc, etc.
Plus, I got to visit Plovdiv that highlights the 19th century Bulgarian revival and Veliko Tarnovo with its 13th century fortresses.
Bulgaria was great. The history, the architecture, especially the people.