In the upcoming 8.3 Patch for WoW, they are changing their AH system so that you can tell the AH how much of what crafting material you want to buy, and the AH system will go through the cheapest items and give you a price quote and you click Buy and voila. You get the items.

For example...

You want 150 Iron Ore.

There's Player A who has 50 of them listed for 1g each.
There's Player B who has 75 of them listed for 2g each.
There's player C who has 200 of them listed for 2.5g each.

You tell the AH system you want 150 Iron Ore.

1). It will grab 50 of them for 1g each: 50g
2). It will grab 75 of them for 2g each: 150g
3). It will grab 25 of them for 2.5g each: 62.5g.

And it will tell you that you must pay 262.5g for the 150 Iron Ore.

I'm rather excited about this system and I wish we could have something similar in FFXIV.