I've been thinking about doing this for my subsonic reloads.Found a guy who converts .223 cases to .300 Blk out cases for 8 cents per rd. Can't find the link but I think it was through Selph Arms. I've got 1k LC once fired cases I can convert. Dies and trimmer and I won't need the commercial stuff after all.
I've been pricing components and it's also looking like you can get it down to about $0.40/round fairly easily if you reload; even lower if you get some mil surplus bullets (frangibles). On subsequent loads you're probably closer to $0.30 since you can re-use the brass.
I feel ya country_boy. I have a 300blackout upper on backorder, but already have the dies ready to rock. The wait is killing me. Maybe I should start cranking out ammo until it gets here.