Big problem

[jrigheimer]

Driving down the highway at 65 for about 70 miles, suddenly the oil pressure went to down to zero in about five minutes. Went for the exit and right before I got to it there was a pop and grinding noise, pulled over and there was a cloud of white smoke. white smoke came out of the air cleaner and exhaust. Tried to start it again and heard a grinding noise so I didn't mess with it.
Got towed to the nearest chevy dealer because everything was closed. what could this be, maybe a head gasket or oil pan. What caused the grinding noise. How did this happen in the first place. Will it be expense .

Thanks