Just because your transmission is leaking does not mean it has to be rebuilt. If could be as simple as the pan gasket leaking, or even just loose. If this is the case, it should be relatively inexpensive to repair the leak. If it is a seal on the front, right behind the torque converter, then the transmission will have to be extricated from the vehicle in order to replace it. In this case it will be expensive to repair. It could also be a cooling line leaking. It will be necessary to take the car to a repair facility to know for sure.