You shouldn't compare what you have with Flaming River. It's not so much their completely rebuilt units as it is their warrenty and liability.
The condition of yours matters where it be from a 67 or a 76. If the input shaft moves nearly an eigth of an inch in and out of the housing you have a 100 dollar usable core at best. A parts yard might want 200 for it but most of those include a 30 day warrenty.