Attempt to move the flywheel firmly up and down to determine any play.
If there is no compression then you are looking at new rings and maybe new bore and piston.
If there is play in the crank bearings as well, then you are looking at a complete tear down and possibly a need for the machining and installation of crank bearing inserts. Then factor in new bearings and bottom end rebuild kit.  Factor in labor as well.
This may be costly if you aren't able to do the rebuild yourself.