It's very very easy to be cheaper than a helicopter. Drones can require zero or minimal labor, move fast, and run on electricity.
If we can have them carry a decent weight and have good reliable ways to get them from and to where they need to go, they will revolutionize delivery. Door dash will be obsolete.
In addition, the Amazon/DoorDash model isn’t even what we’re talking about here - this is a predefined, specific route with the last mile still handled by conventional vehicles, so it is even worse.
If we could all have landing pads like we have mail boxes, something with a fence, it would be much better.
You don't leave it free space because then you have all sorts of drones whizzing around in all sorts of random and uncontrolled directions and that creates a lot of clutter that will cause crashing.