I'm inclined to say no to buying fish with ich or any other disease for that matter. You're putting your entire tank at risk. They would have to give those fish away before I might consider taking it home. And I don't have a quarantine tank so it's not at all worth it to me.
Plus, even if they do give you a "nice price" you're still going to have to buy meds and stuff to nurse it back to health, so in reality, how much is that fish costing you?
I know it's hard to resist saving fish in a bad situation, but buying someone's diseased fish isn't going to encourage them to keep their fish healthy in the future. Instead of trying to cut a deal, how about you tell the employee that you would buy his fish if only they weren't sick. And if they don't care about getting their fish healthy and keeping them that way, then just stay away from there.