That would yeah, like most, that would be the Game time token. It has gone up quite a bit within the last couple months.
I'm pretty sure it was the Reins of the Swift Spectral Tiger, though I don't remember how much I paid for them, probably between 300k and 350k.I'll add my almost-but-not-quite most expensive purchase, which was Recipe: Thistle Tea. That's right, the non-BOP version. Available on the AH. In 2015. I saw it for 800k and decided I didn't want to literally empty my treasury on any one item, no matter how rare and how much I wanted it. Then a few days later it drops down to 600k and I foolishly decide to wait until it drops down even more. I never saw the recipe again.
My most expensive purchase was definitely a BoE belt from Highmaul to complete my Paladin's transmog. It was around 200k at the time.
Most expensive purchase wasn't necessarily just 1 item, but when on a spending spree. Bought bout 8 TCG mounts I didn't have and spent a few million gold back in WoD.
My purchase of Minion of Grumpus cost me around 100k!
I remember saving gold back in the early days when it was still hard to come by and stockpile. My largest AH purchase (accounting for inflation) was Battered Hilt back in WotLK. I actually took out two loans of gold from guildies to be able to afford it and spent the next month paying them back. No regrets.
The most expensive purchase was a jeweled onyx panther for 80k lol. Got a really good deal on it. I would love to not have to buy WoW tokens in 2 weeks when my time runs up. I think I will be buying a minion of grumpus when I farm again :D.
The most expensive thing I've bought is probably a WoW token at the current market rate. The inflation is crazy!
The most expensive thing I've bought is my first WoW token, 150k gold+ is a fortune for a new player lol.
Mascot and mounts bought many of them and always killed my in-game wallet XD
Vial of the Sands I think :) well, there were few more mounts I bought over the years, maybe there was one more expensive. but we can say for sure it was a mount...
In Legion I have bought nothing pricy on AH, but during WoD I bought modules for AH bot for garrison, a couple of pvp ones were crazy expensive on my realm
My most expensive AH purchase was the Depleted-Kyparium Rocket. I have forgotten the total price, but it was nearly two thirds of my total money at the time.
In terms of relative gold value and not actual gold, the mechano hog back in the day
Back in Mists of Pandaria I've bought Sunstone Panther (really matching my current transmog). I didn't have much money and someone posted it a few k cheaper than others, so I had to.
Most expensive purchase is surely a mount, I'm just not sure which. One of the jeweled panthers or the sandstone... it's been too long to remember how much I paid, but I know I would've been willing to hold out for a deal XDMost expensive non-mount/pet type purchase would probably be recipies. I'm a bit of a completionist so willing to splurge a little. Wish I'd ever seen a Thistle Tea (though not sure I could make my scrooge-y butt splurge -that- much).
The most expensive thing I ever bought off the AH was the Grinch mount the year it released... I farmed for weeks, daily on 10+ alts and couldnt get it so I splurged and got it a week later off the AH for like 100k... Now the more expensive thing I buy is a token every month as it slowly rises to the point that I cant afford it...Most expensive thing I sold was the Toys and Mounts from Shadowmourne Questline. My hubby and I would take turns getting it on alts and then selling them on the AH with a profit split. Before the toy box they toys could easily go up to 100k but the mount still does.
My biggest purchase was Jeweled Onyx Panther! I bought it with a huge discount)
The most expensive thing I purchased in AH was overpriced reagents a very long time ago. I absolutely needed them for one of my professions, and ran out. I didn't feel like farming them, so I just went to buy them. They were Motes of something, and I have since farmed so many Motes of everything that I never have to buy them from AH again.
The most expensive purchase in AH i ever had was the Glorious legplates, it cost me like 150 k, fortunately the rest of the set i obtained via salvage yard from the garrison. I´m happy that i dont have to buy that again since all my chars who can equip plates can transmog it.