You might try this load: http://www.paraklesetechnologies.com/proddetail.asp?prod=20GA234BB%2F25
At a little over a dollar a shot, it's cheaper than the non-toxic waterfowl loads, which would be another alternative.
FWIW, I've killed a dozen or so coyotes out to 45yds with #6 and #5 birdshot (turkey loads, 1-5/8oz 1250fps) out of an xx full choke. Drops them like a sack of schit.
