Still Ned to grow a plant to supply so the amounts are the same. Perhaps at the money figure changes.

BTW, not sure if you have or not, but I have, and it ain't that easy, in fact it is quite difficult, to produce your own high quality cannabis.

Around $200 for 8 ounces, give or take.

And it is easy once you learn how to do it.

And it ain't easy to grow high quality cannabis. Not retail sale quality. All the new strains out every year which means if you don't have the latest you have no product. Or you want the newer strains so your grow doesn't measure up.

Then there's all grow bags, Nutrients, soils, clones, drying racks, water etc and the information you need aren't cheap.

I've done it, on large scales and backyard types and it ain't easy at all. Rain (this last year especially) deer, spider mites,mold and the fact you cannot leave your plants for months at a time make it very difficult.

Then there are the various municipalities and ordinances that severely limit or outright ban backyard growing. Some are complete bans.

You left out that it is hard labor, especially when you are aged or have other challenges.
As for the math, I think only 25.6 are over 18 and I was too lazy to compute the over 16 population.

With good genetics and a moderately green thumb, you can do it. It requires space and some investment.