You're in the golden age of 9mm GG. At around $260 to $270 per 1000 round case, I don't see it getting all that much cheaper. Remember that when we had the severe ammo shortages back in '16-'20, *all* pistol rounds were $0.50+/round if you could even find them...
When the next bout of inflation hits, we'll look back fondly at today's ammo prices (remember, energy always leads the inflation train and with diesel topping $4.25 a gallon now here in NM going into the winter heating season, I suspect we'll see $5.00 a gallon before too long. Natural gas is almost at $4.00/million BTU and the cold season has yet to even start, we may see $12/mmBTU spot prices if this winter is really harsh like some believe it will be)
I think P32 is definitely on to something in that Winchester is only offering such a large rebate due to the fact that they have *way* too much inventory already on the shelves of the retailers (hence retailers aren't buying more from the factory) and they need to drain it ASAP, but the only way to drain inventory that has already sold and is a set (high) price is to rebate it. That's a double edged sword: good for now because who doesn't like seeing "35 cents" per round M855? Bad for later because any future batch of M855 will be much more than that for the factory to turn a profit or at least break even.
Once demand falls due to high prices the retailers can't sell & make their profit and/or the manufacturers can't sell and make their profit. Eventually one or both start going under/get bought out, the industry consolidates, and only the retailers/manufacturers that can make a profit at lower prices remain.
Bottom line is we are in one of those golden ages of ammo where selection, availability, and price are all fairly reasonable but it won't last forever.