I don't need expensive shells to kill ducks. I shoot Winchester Xperts in #2 or BB (3" shells). That's what I can get the cheapest.
It is not about how expensive the shell is, it is about learning to use decoys effectively, proper concealment and good calling to put the ducks at a proper distance in order to make clean kills.
We effectively put ducks in the 15-25 yard range every day we hunt.