The "Shut up and take my money" Achievement requires that you buy one of each item from merchants. There are a lot of items on the list that my class doesn't use, and I am unfamiliar with. Is there one vendor, or a short list of vendors I can go to in order to buy one of each of these items types? Also, since I plan on just selling many of them right back since they are of no use to me - generally, where can I buy each item the cheapest?
When I started doing this I checked vendor for white items each time I was in town to sell. Since white items costs only for a few hundred gold compared to the blues which costs over thousands. However what I found was you had to buy blue rings/necklaces. As of now I am having trouble finding a merchant that sells Spirit Stones.
Also a tip is to buy it on normal mode since those are the cheapest and you might consider buying the blue ones there if you don't want to wait.
If you want to farm this, you might want to go to A2 and start the Evacuation of Caldeum quest. This way, you'll have four vendors all very close together that you can check one after another.
But what I did was just to check for white items every time I stopped at a vendor, and then buy and resell them, until I had almost all of the items checked off, before I started concentrating on the last few.
There's a relatively good guide for this in the comments at D3DB:
NEW TRISTRAM, Tashun the Miner (first vendor you see). He sells: Axe, Sword, Gloves, Boots, Chest, Waist, Legs and Shield.
NEW TRISTRAM, Arghus the Collector. He sells: Wand and Bracers.
NEW TRISTRAM, Radek the Fence. He sells: Bow, 2-Hand Crossbow, 1-Hand Crossbow and Ring.
HIDDEN CAMP, Silmak the Fence. He sells: Quiver, Fist Weapon, Helm, Shoulders and Neck.
CALDEUM BAZAAR, Tilnan the Collector. He sells: Dye, Staff, Spear, Mojo, Magic Source (Known as Wizard Source) and Ceremonial Dagger.
CALDEUM BAZAAR, Lugo the Miner. He sells: Dagger and Mace.
CALDEUM BAZAAR, Squirt the Peddler. She sells: Daibo and Polearm.
DAHLGUR OASIS, in the Rotting Cellar, Javad the Merchant. He sells: Spirit Stone
THE KEEP DEPTHS LEVEL 1, Ironsmith Aldonado. He sells: Mighty Weapon.