Taxis are quite cheap in Romania. The cost is usually around 40-45 cents (1.3 RON) per km, with an extra 1 RON (about 30 cents) for the start. In smaller cities taxis are even cheaper than that. Do also note that in some cities there are special tarrifs for night trips or outer city trips. 

The taxi driver may want to cheat you if you look like a tourist. If so, just tell him to start his meter and you should be fine. You may want to negociate your ride in advance if he refuses to start his meter, but only do that in case you’ve used a tool such as Google Earth to measure the distance and costs. Otherwise, get out of the cab as there are plenty of them to choose from.