But Serbia is an anti-European hotbed of backwardness and Bulgaria is riddled with corruption (in every sector, quite frankly), so I'd rather not cooperate with them. Ukraine would indeed be a problem because of the economic disparity. Poland-Romania market works the best of them all, Romania is like 15% behind Poland in terms of economy (and not 250%), and you don't have to set the threshold much lower in order to sell any product in the other. In Ukraine, on the other hand, it's quite problematic.