I'll bet the radiator costs more than $100, and I wouldn't be surprised if the leak was coming from the top part of the plastic side tank, right across from where the radiator hose connects. Mine cracked in that spot, and the guy at the radiator shop said that's pretty typical - that spot gets a lot of heat, as the coolant coming from the engine is hot. Being made of plastic, over time it wears out and a stress crack forms. I had the side tank replaced for $55 on the advice of the shop (a reputable place in the area). They checked the rest of the radiator and found it to be in good shape.