Did not you ask some time ago by taking the bike all the way across Europe?

More important here is that you need also to REServe space for bike and that seems not possible in all trains. Price then depends on type of train and how far you take it.

Older reports (but thats from some 10 yrs ago) all tell that CFR is/was not prepared for it at all and that most such people ´bribed´ the conductor to allow it. But I have no idea if that is still even possible.

use google: ´taking bike on trains in romania´ and read.