Lot of noise coming from the front

My fiancee has a 2005 Nissan Altima 2.5, last month when she was driving she complained that there was lot of noise coming from the front, we thought it should be some loose mechanical part. But after a while the noise got louder and she had to stop driving the car, later when we took it to a local mechanic we found that the car was driven without the engine oil, we have no clue how the oil got drained or if the engine oil wasn't replaced at all the last time we took for service. The result is one bent piston rod and broken lifters in the engine. The mechanic says the engine has to be replaced as such either new or used ones, which is going to cost a lot for us. Can you give me any other possible solution in this case?