The place I order my reloading supplies from has 000 buck (.350 diameter and 64 grains) at a bit over $15 for 5 lbs, which works out to about 2.7 cents each (before adding the shipping cost). The same vendor lists .350 lead balls at about $6 per hundred, which is obviously more than twice the price. I don't know much about cap and ball revolvers, but if your 36 Navy uses .350 balls I can't see any reason why the buckshot wouldn't work just as well, assuming you shoot it enough for the savings to be worthwhile (there would be about 550 balls in 5 lbs.).
