I had no luck tracking down anyone in the 300k-700k gold range, so I'll just muse a bit on what it's like to play with 450k gold.
Nothing on the AH is out of my price range. Reins of Poseidus has been
on the AH for a bit, at 75k. If I wanted it, it's mine. I could buy 5. If I spent like that, though, I'd run out.
I buy or craft BoE gear for my new 85's (I look for a deal though), fast flying for all, Stonedrake for my Priest (She earned it most) but not anymore than one, since it will be account wide, a Chopper for my Hunter Engineer, self-made, of course. I bought a few guild banks for good prices, maxed out the tabs, and started stashing for Mists. I always buy frugally, and I think that's part of how I got this
far, but for a while I was feeling the expense of having 5 85's to fund.
The only dailies I do are Cooking and Fishing dailies on a few alts
for points and TB dailies on my Pally for the trinket. Dailies are just
not good gold per hour. I also don't do dungeons after the VP cap, since
I see that as a waste of time.
I level professions for new 85's from scratch, usually costing me no more that 6k-8k gold. I see dropping a maxed profession as inconvenient, but sometimes worth the loss. Since I have one of every crafting profession, the only things I buy from other people are potions and flasks, since I am not specialized in those, and they sell below cost-of-mats for non-specced Alchemists. I also buy VP BoE's since I prefer to trade my excess Valor for Conquest, for whenever the PvP bug bites.
I'm at the point where making gold has become it's own game, so driving up the number is a source of inner satisfaction. I have long term plans for the Mists mounts, of course, but that's a ways away. I'll also be taking full advantage of Glyphmas to come, along with the new DMC trinkets. Honestly, I think I might double cap a few months into Mists.
I think the minimum I could play comfortably at would be about 2k per max character per week after an initial large amount of spending when hitting cap (maybe 10k?). So I think, and this is just conjecture, that I'd want about 20k on hand and about 10k a week income, if I played without gold making as a priority.
I think there's no real upper limit to how much I'd be ok with having, since anything after 100k is just a number to me. My first 100k was the moment where I first really felt I could hit cap, since going from 10k to 100k was a short, steady grind, and I believe going from 100k to cap will be a long, steady grind, but not 10 times as long since I perceive an exponential aspect to gold making.