Datacores are worth what datacores are worth.
If you think they’re too expensive to buy, so you “mine” your own instead, you should be selling them instead of using them because it has the exact same value regardless of how you source it.
That said, on a conceptual level the idea of sourcing your own datacores for anything but the smallest operation is fairly ludicrous. If every one of my characters had maxed out research agents, and I spent every waking moment running sigs, I still couldn’t keep myself in datacores.