2000 Ford Taurus Head Gasket

Some weeks before my Taurus broke down (it won't start), the antifreeze started to leak when the heat was turned on. Then, some time later, I began to notice heavy white smoke coming out of the exhaust. I thought this was because of the cold weather. But a few days before the engine stopped, I noticed fluids spilling from the exhaust pipe. There is no antifreeze in the oil. I think the problem is the head gasket, but I don't know. A mechanic suggested replacing the engine to a "low mileage" one, since this would cost only a few hundred dollars more than fixing the head gasket.