Need some opinions

My car stalled on me monday,,,,i heard a slight knock in the engine after I started it up... I was almost to work driving 25mph, when the rpms jumped to 4k and the engine wouldn't move at all. I shut it down, and the motor started leaking antifreeze, and i had white smoke from under the hood.

My mechanic said that the flywheel cracked or came a loose, I have never heard of such. He said it would cost $739 to fix.

I only paid $200 for the car and put the motor in myself. Would it be worth it to pay $700 and then still maybe need a head gasket...

Any comments are appreciated.

I've seen the torque converter bolts apparently loosen although it made a banging noise. Since you installed the motor, that's something to check.