And thank you very much for the warning about the tray hole. I don't know what to do about it. Like someone else noted, emptying a tray so large would not be easy... But I have the room, so using three trays is fine, it's the price that is the issue.
Garden Trays come in various sizes - Worth looking at if you think photographic trays are expensive.
As for drilling large holes - Use a hole saw, and don't try it on an old tray. Most plastics become brittle as they age.