There are several ways to get from Sofia to Bucharest: plane, train and Bus.
The direct train from Sofia to Bucharest seems to be suspended on the moment. There is a possibility with a stop-over in Ruse.
Starting from April there is a new bus connection from Sofia to Bucharest and vice versa: Flixbus.
Prices are starting from 12 euro single direction.
Departure twice a day from Sofia central bus station at:
Departure twice a day from Militari bus station at:
Sofia central station can be reached with the blue subway line:
Militari Bus station in Bucharest can be reached with the red subway line: