Back in the day Midsouth, Grafs, and Powder Valley would have the best deals. If I was buying in quantity, they'd be the go-to places for primers and powder. Midway and RMR would often have the best deals on the bullets I wanted, but I wasn't buying 9mm or 223, nor was I buying fired brass, so there are other sources for those.
Since things have changed, there's no consistent sources for anything nor is there consistent pricing. Cabelas, Scheels, and Sportsmans can win against hazmat and shipping that others charge, but if I'm buying in bulk, Powder Valley and Midsouth can still win. I use ammoseek, but it doesn't have all the sources. I check Brownells, Midway, Midsouth, Natchez, Grafs, and Powder Valley. There are also a lot of smaller sources that ammoseek and other bots will bring up.
Deals are where you find them. I'm trying to buy primers right now, but a lot of the local sources have a limit of 1000 and I need a lot more. I can get quantity at 10 cents, but I'm looking for under 7. I found 6.3 cents for SR earlier this month at Cabelas and bought many thousands, but they haven't fulfilled the order yet.
I've bought about 6 pounds of powder locally and paid way too much (~$50/pound). Once I've done load development, I'll buy powder in bulk (~24 pounds). If things are similar to the way they are now, that will probably go to Powder Valley.