Free: Contests & Raffles.
Cow calls during modern firearm can be used but due to the numbers of hunters on public land and, more importantly, the number of cow tags given out I use it sparingly. I've jumped elk before and stopped them with a cow call to get a shot. One bull stopped three different times as I was chasing him up a hill before I got the shot. The bull I shot last year I stopped with a cow call as he was heading over the hill in front of me.
Elk are vocal all year long, bulls are more vocal during the rut which is september into mid october. Bugles will probably only be effictive during that time. Cow calls will work all times of year since elk are a heard animal, but harder to call them in outside of the rut.