I've got some code working locally. I assume it will solve the issue for stores with a million items stocked, since it only sends prices for repriced items, though I can't actually test that.
The main reason I haven't committed the new code is that updating prices no longer updates everything in the store. The only way to do that with my current code is to close and reopen the Store Manager. I tried to add a "refresh" button, but I don't know how to add a third button there without starting from scratch (using a different type of Panel for StoreManagerPanel, I think), and I didn't really want to get into that. Replacing the auto reprice button would be trivial, but I expect someone would be upset about losing that button.
The main reason I haven't committed the new code is that updating prices no longer updates everything in the store. The only way to do that with my current code is to close and reopen the Store Manager. I tried to add a "refresh" button, but I don't know how to add a third button there without starting from scratch (using a different type of Panel for StoreManagerPanel, I think), and I didn't really want to get into that. Replacing the auto reprice button would be trivial, but I expect someone would be upset about losing that button.