What is the cost, for those of you who cast, to cast a 124gr 9mm round?
Really hard to say. It depends on how you want to measure your costs:
1) Raw material - scrap lead, wheelweights, etc.
2) Equipment - furnace, mold blocks/handles, sizing dies, bullet lube, etc.
3) Electricity to heat the alloy
4) Your time
I've been casting for many years but I've never kept track of my total $$ outlay nor the amount of bullets I've cast, so I really can't give an accurate estimate. I will say that many of my handguns have seldom seen a factory round, and I've fired thousands and thousands of rounds over the years.
If I were to try to compute my cost per cartridge now I wouldn't even factor in the cost of my cast bullets. I figure the equipment has long since paid for itself and most of my scrap metal was purchased (or obtained for free) back in the 1980s. My dad and I once bought several hundred pounds of range scrap for about about $40, but those days are long gone. I'm still casting from some of that material.
I look at casting as a hobby by itself, so I don't put a $$ cost on my time. The real benefit is that I shoot a whole lot more for the same amount of money that I would have spent on factory ammo.