you would have to beat stuff like this which is primed and unfired at $1/each:
https://www.grafs.com/retail/catalog/product/productId/88965
And this, polished once fired for $0.85 each:
https://capitalcartridge.com/50-bmg-rifle-brass-200pcs-washed-and-polished/
115 lake city for $0.90 each
https://www.armorally.com/shop/50-bmg/
similar lake city, polished, here:
http://reloaddepot.com/product/50-bmg-fired-brass/
And that's just the first page of google
There are a lot of options for once fired 50 BMG brass, everybody has it in stock, so it's a dime a dozen (figuratively). Guys like me that are serious about reloading 50 BMG are just going to pony up $5 for new RWS or Lapua cases (for their superior internal volume consistency). We're firing a $3 bullet propelled by $1.70 of powder and ignited by a $0.70 or even a $1.00 primer. We are not going to put all that money into a pickup range case from God knows what chamber.
Consider also you can get AE XM33 ammo for about $3.50 each, and that contains, nominally, $1.70 in powder, $0.70 in primer (CCI 35), and $1 bullet. If you buy this "plinker" ammo, you get the LC case for
free.
So your market is the plinkers and the poors, and you're not going to move it unless you let it go on the cheap - because with loaded ammo available for $3.50 each, once fired LC cases are basically worthless except to the guy who got them free with loaded ammo that he shot