I would stage any keeper fish in a filtered, aerated container (for me would be an above ground pool size dependent on size and number of keeper fish). I would go through my pond after lowering to select all fish I wanted to keep. One reason is what you have referenced - price. If I can identify health and desirable forage fish, why toss them only to repurchase them? I've already got X number of them, I'll stage them until the pond is cleaned and refilled. I also understand the value of predator fish, so again, I would either donate to food shelter, sell to others, or stage them until the pond is ready for their release.