What is a 51 ford 239 flathead worth?

How much can you pick up a running one for that needs a good rebuild???

 

If it's not running and you can't remove the heads to check for cracks....$100.
If it's running $500 max.

 

I picked up a very healthy and good running one for $500 and that included everything from the fan to the bell housing.

 

Its worth what ever some one is willing to pay. Who decides????