Chapman might be a little rich dollar-wise, but would cost far fewer prospects. That allows you to use some of the ones you save for a stater or maybe more relievers.
So that's another aspect to this. Do you want to give up less for just this year? Maybe, maybe not.
For instance, I think Sonny Gray or Michael Wacha could he had for a minimal prospect return. But they're both older and gone after this season or next season. On the other hand, Reid Detmers will cost more, but he will still be in his prime and under arbitration when Sykora, Susana, and Rosario are in the MLB rotation.