If you are only going to be shooting the Holy Black- reloading is the easiest way to go.
All you need is either some Magtech (balloon head) or the heavier Rocky Mountain Cartridge (machined from bar stock) solid brass cases in 16 bore, some primers, wadding from Circle Fly, your favorite brands of black powder and shot and finally some rubber cement or sodium silicate to seal the end.
The brass cases don't really ever wear out if you use them in the same gun with black powder, and you don't let them corrode after shooting them.
Your loading implements need be nothing more than a hammer, a dowel of a size that will go in the hull, a punch to deprime the fired cases, and a hard surface to seat the new primers on- but just spend the money on a 16 gauge size shellholder from RCBS or CH-4D that will fit onto a hand primer to seat them fully.
You can get really fancy and buy a three die 16 gauge full length die set of 1.25" dies from CH-4D for $187.50 if you are going to shoot hotter loads than black powder out of them, or may be using them in more than one gun or need to slightly roll crimp the end for use in repeating firearms.
Costs to get started loading brass hulls:
Two boxes of brass (50 rounds): @$50.00 shipped from any online source
25-pound Bag of magnum shot: @$35.00
Various wads from circle fly: @$20.00
Brick of primers: @$40.00
Pound of black powder: @$25.00
A rough total of $150-175. to get started.
It depends upon how much you are going to shoot the old gun, and or how much you value being able to be independent of companies that supply a very specific product. Heck, you would have the freedom to load any shot you wish rather than just the #6 or #8 shot that used to be offered. I shoot a lot of #4s, #2's and #00's myself.