I would think a calendar might qualify as media mail, which is usually the cheapest method of all of them. You might want to ask your local postal clerk. I just received a book I ordered on eBay and it was sent media mail. Got it in 4 days from when I ordered it.
That’s a good thought, as I used to send calendars to many relatives as gifts. I cut back on that because the shipping by 1st Class Mail was as much as the calendar. :-(