This app was mentioned in 7 comments, with an average of 2.29 upvotes
You can use the mobile armory app (which is free, links below) to buy these up quickly, with just a couple button presses.
Search for your item, set results to show "buyout only," and let it search. If it finds say 200 single-stack ore by the same seller at the same price it will list them as a single line-item in the search results.
Click on it and it'll ask how many of them you wish to purchase, press "Max" and you're done. It'll buy out every single one of them for you.
Note: You cannot be logged into the game and the mobile armory AH app at the same time.
You can still download here, but it's no longer functioning.
https://play.google.com/store/apps/details?id=com.blizzard.wow
They redirect you to the following that mentions they'll be rolling up armory functionality to the new BFA app. Wasn't. Spreading. Lies.
It lets you gchat, AH, and look and pose your alts on the go. Its also on IOS
There's always the official app...
This actually IS possible. You have two ways:
As you can see, the task is far from trivial.
The funny thing? They removed the Armory app listing from the Google Play Store. My wife and I progress slowly, and we're currently in WOD. Can't use the Legion app because it won't let us select any characters. Can't use the Armory because they removed it. I no longer have a WoW mobile app.
Blizzard put the cart before the horse on this one.
For anyone else in the same predicament, you can no longer find the WoW Mobile Armory on the Play Store by searching it, unless it's already installed. So, here's the direct link.
EDIT: And the Armory app no longer even works...