It's only cheaper (maybe) if you cast as well.
I was paying 50 cents each for my Lyman Sabot Slugs.
I wanted a load, for competition, that had less recoil, but alas, I only found that the full house loads gave me the accuracy that I required.
I still load slugs on a MEC700 Versamec, made in the '70's.
Everything is the same up to and including inserting the wad, then you remove the hull and insert the slug into the hull/wad, making sure that you don't fold down a petal, then crimp on the press.
I enphasize the installation of the slug, because a friend of mine loaded some slugs and got a petal folded and upon firing split the barrel on 2 sides of the barrel plus a bulge at the splits.