hi gheko, i wouldn't recommend attempting a Greenfeild drive rebuild with no
previous experience, while they are simple machines, the drive setup has to
be done properly for it to function right, with grave consecenses if not.
all parts should be available, but the cost will be high if it's flogged out as you say.
( expect $400-$500 as a guide ).
it's not uncommon to find cracked frames and flogged out front ends etc, they
are tough machines that are generally cained for many years, so able to be repaired to cost
ratio will be totally up to you...
just keep in mind that old flogged out machines arn't worth that much anyway..