It actually cost me LESS to load buckshot than birdshot.
But then, I make my own buckshot.
For 00B, I use a Lee single cavity .330 roundball mould. I can cast about 300 per hour. An hour worth, lasts me a couple of years.
I use a .310 RB 2-cavity mould to make a roughly 0-1/2. It is larger than a #1 (.300 nominal) and smaller than a true "0"-buck (.320).
I have found the best use for the smaller (.310") is to load them 2x2x2x2x2, for a 10-pellet load in a 2-3/4" 20ga. load.
I use 16.2gr of Hod.LongShot, over a Remington RP-20 wad with the petals cut off even with the cushion. I use Jim Dandy Grits as a buffer.
It is easier to load than it sounds.
Patterns to nearly 100% at 40yds.
My Huglu SxS double with Modified choke will put 10 pellets into a paper dinner plate at 25yds. I have killed one doe, and two pigs with this load.
Cost of pellets, perhaps fifty cents a pound.
MUCH HARDER AND ROUNDER THAN PURCHASED BUCKSHOT !!!
For 12ga I use a similar load utilizing a Win AA- Red wad and 12 pellets over 32.0gr of HS-6.
Have never seen the need or desire to develop a 3" load as these perform perfectly.
(UTILIZE DATA AT YOUR OWN RISK. SAFE IN MY GUNS, UNDER KNOW CONDITIONS.)