And the Falcon 9 first stage has nine engines, so that's about 9-14 million dollars worth of engines for the stage. That's in the ballpark of a quarter of the total hardware cost of the booster, and that almost certainly doesn't include the testing overhead for each engine.

Anyway, my point is, even if all that SpaceX had to work with for reuse was the main rocket body and a pile of the majority of the engines in working order, that would easily add up to tens of millions of dollars worth of equipment, and thus tens of millions of dollars of cost savings on reflight. There's practically no way that reflight could be more expensive than a new rocket, there's just not enough complexity in the vehicle for that to realistically be possible.