Do you have a specific purpose for buying finished cast lead projectiles?
I got into casting lead figures for RPGs before I ever cast bullets, so I had half the gear & experience before I started making projectiles. So casting my own bullets sort of came naturally to me. It wasn't until I was DEEP into it that I figured out I could produce my own projectiles and bring my cost per round down to about $0.04 after buying powder and primers in bulk.
My lead bullet use is because I love the craft of making different projectiles. And I can customize to any need I imagine I want to fill.
But, at the end of the day, it isn't about cost or the desire to be able to stand alone apart from bullet manufacturers. It's about me being a maker and craftsman in my own right that I make my own custom projectiles.