Or, you can reload your own, which I think is what you had in mind.
I calculate you can reload a box of 25 3 inch shells for around $15-$16 assuming you have a reloader.
If you don't, you could get one commercially for around $100 or so. Doing this, you would pay for the reloader with the savings. If a box of 25 Bismuth (commercial) you would save $20/box and pay for the reloader after 5 boxes of shells. Or, buy a reloader from eBay or elsewhere for around $50.00 and pay for it within 2-1/2 boxes of shells.
Bismuth shot can be purchased in just about any size you prefer.
Ka6otm