On the other hand, megawatt chargers might get cheaper rates because they're buying in bulk, and it's (generally) easier for power companies to provide service

On the other hand, megawatt chargers might get cheaper rates because they're buying in bulk, and it's (generally) easier for power companies to provide service to one big customer than a hundred or a thousand little customers. (That's assuming the infrastructure in the area can accommodate it. I expect any heavily-used truck charging stations are going to be located where the utility hookups are comparatively cheap and easy.)