Where can I most efficiently buy all items for the "Shut up and take my money" achievement?

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.

Spirit stone and mighty weapons will not be sold from regular town vendors , but only the random spawned vendors

You can get a mighty weapon from Kyr the weaponsmith. He appears during a random event. After passing through the Halls of Agony level 2, you will sometimes find him on the highlands passage. Complete his event and gain access to his shop, where you'll find a mighty weapon for purchase.