Free: Contests & Raffles.
One method that has worked well for me on public land is pattern/ambush. Think of it like deer hunting. Watch the path the birds take to/from their roost site and pick a spot on that path. If there's a clearing or a bench on a hillside that you see the birds at near there roost site try to identify that and set up there. I've found birds in these types of areas in the evening on their way to the roost then set up the next morning and had them come back there after fly down to regroup or start their day or whatever. I'll usually call very little if at all when employing this strategy, maybe just some soft yelps after fly down to get their attention. I've shot several birds without calling at all this way. If your already where they are heading your odds increase dramatically.