There are several data points available with which one can make at least approximate calculation:
- The price of a Falcon 9 launch is $62mil (was expendable up to now)
- Gwynne Shotwell said that if first stage can be restored for $2mil, then the reflight would cost $40mil
- The cost of the first stage is known to be around 70% of that of the rocket
- The cost of the rocket is only a part of the F9 launch cost. Let's say that this fraction is R.
- Given that a reflight uses again everything else other than the first stage, from the above one can calculate:
Reflight ($40mil) = Stage 1 restore ($2mil) + everything other than Stage 1 ( $62mil*(1-0.7*R) )
Taking into account the uncertainties, this gives you that the cost of rocket R is between 55% and 60% of the full launch cost.
Having these numbers one can make a ballpark estimate for the cost of FH and the FH reflight. Those are the numbers listed in my previous message.