I usually don't buy large ticket items on the AH, but back in the day (well before TSM) I was looking for one of the crafted Katanas that blacksmiths can make. There were a couple on the AH from the same crafter who had reasonable starting price bids but ridiculously high buyouts. I intended to bid but was distracted and, as you can probably guess, hit buyout instead. After the purchase I had 7g to my name but a pretty sword.
Well for me its the Sandstorm Drake . I bought it for 45k gold back in the day , I like to farm my things on my own . That is my story :(
I don't usually buy expensive items on the auction house. My most expensive purchase was likely a Depleted-Kyparium Rocket for just south of 100k.
Most expensive thing would probably be the trading card rhino for my hunter. I love that it's rare and looks like no other mount.
I dont really buy alot from the auction house these days, but i think the most expensive item is Hatespark the Tiny pet for about 200k, I also spend most of the gold on the BMAH on the Unlclaimed boxes for around 200k-300k each to have a chance to get some rare mounts to my mount collection.
I bought 5k Chaos Crystal for 1kk and 175k Arkhana for 1,5kk and then crafted from a Enchant Ring - Binding of Mastery to Obliterum. With this method I received a 2kk profit! It was unbelievable for me. Then I bought Reins of the Spectral Tiger for my friend because I like the other mount Cindermane Charger.
Not counting wowtokens, my highest bid was 7K and highest sold 15K. I usually just sell extra stuff, that I habe no use. Pets are a steady supply of small cash.
Before the WoW tokens appeared in the auction house, my most expensive purchase was probably the Vial of the Sands 2 seater mount. There are still many expensive mounts and pets waiting for me right now and I could buy a few of them finally if I didn't need to spend most of my gold on the monthly token. :)
Well the most expensive item I bought on the Action House were wow tokens.
My biggest purchase at the time was the Meknigeer's chopper for 8k. I was a noob who started in WOLTK and i wanted it so bad, so I farmed endlessly to get it. And i have no idea how to make gold. :D
I really enjoy posts. Best was the one with human mistakes. Once I purchased by mistake some leg mail with buyout 89k. Frustraiting, but we have to move on :)
My most expensive AH purchases are TCG pets, paying up to 200k for them atm. Should have bought them some years ago I guess, but oh well: better late then never :-)
I dont really care about fancy mounts/pets so I never really spend more than 20k on the AH, for a BoE or something like that. Thats ofcourse excluding the WoW token ¯\_(ツ)_/¯
most expensive must have been priest T3 chest it was the last i needed for my priest and not a single one showed for over a year (WoD) ended up on 720k
the single most expensive item i've ever purchased was "cord of pilfered rosaries" titanforged ilvl 940. bought it for 250k, and after many weeks, finally resold for 332k. that was the scariest investment i made so far i think. sooooo glad it sold. >.<
Thanks to a mistake i bought 15 eggs for an achievement cooking for 520k... (current price 15s each..)
My most expensive buy from auction house, I believe, was a pair of 930 haste versa boots for my Prot Pali 5days into ToS. Carried me for over a month, so gold well spent I think
My first big sell on the AH was just after the crafted legendaries were released. I managed to sell it for 91k. I've never had so much loose change before so I splurged for the first time in my WoW lifetime and bought a Sapphire Panther. Now I'm only missing Ruby and Onyx, but I still regard my Sapphire panther very highly. :)
Other than 900K+ for a BMAH no-longer-obtainable mount & a toy, I've dropped 800K+ buying no-longer-obtainable primal leather to craft one of the Zul'Gurub sets for transmog (and still a few leather short as they got too greedy & I couldn't afford to buy the rest).
My most expensive AH buy was Vial of the Sands, which cost about 60 000g at the time.