Prismatic topper *should* be worth the most, as there is only one of it in existence generated as a prize for Latisan Sklay via the GMs, but high end items are worth what people will pay and that could make any number of items worth the "most".

triple max UV'd BKR anyone? I believe i saw some dude selling it close to 95k energy in /2 once, also a bkr is much more expensive than a gatecrasher helmet I think

Dreadful auras have gone well over 100k ce; 125k ce was the go-to price on their release and I've seen them go as high as 175k ce. Darkfang shields can easily approach 400k ce. Iron dragon wings on release went for $400-500 via steam and paypal (though they've since been put on flash sales for significantly less). Wings of summer, on release, went for 100-120k ce (although those have now dropped significantly in price). Orbit aura, on release, went for 100-125k ce. Node aura, on release and possibly still now, went for 100-110k ce. Prismatic shoulder boosters would be absurdly expensive if ever unboxed, as the accessory is part of a 1% tier and would hardly ever be unboxed as prismatic. That may become the most expensive item possible to obtain normally if ever unboxed.

If you wanted the most expensive set possible, you could use:

Prismatic chapeau with prismatic giga shades + mechtennas

Black kat cowl w/ Shock, Stun, Fire MAX with prismatic giga shades + prismatic devious horns + prismatic scarf (these items may well look awful!)

Black/white rose tabard with prismatic shoulder boosters, dreadful aura, freeze/poison/shock/curse vial bandolier, prismatic ankle boosters

Black kat raiment w/ Shock, Stun, Fire MAX with prismatic shoulder boosters, dreadful aura, freeze/poison/shock/curse vial bandolier, prismatic ankle boosters

Darkfang w/ Sleep, Shock/freeze, Fire MAX (although that would now be impossible to get unless any already exist!)

Four Mixmasters/Celestial sabres w/ASI, CTR, Undead damage MAX (in the case of mixmaster, undead would be the ideal UV. In the case of sabre, it wouldn't really matter.)

Gun pup sprite w/ t3 harness. Fed only zee cores to get lv 105.

Yeah, I know of at least 2 people who have them on a set. It's not the most visible aura, though - a prismatic bubble patterned like the other node items that pulses from the middle of your character

Well yeah, you can always roll the best UVs possible and attach other rare accessories to some item and say "DONE. IT HAS ALL OF THE RAREST STUFF!" but that's kind of cheating the system a bit.

Also, a Darkfang shield w/ sleep + 2 other status UVs would be much rarer; the window of opportunity where you could craft that was tiny but existent. Putting poison, stun, freeze or even curse would be better than putting fire/shock on it as well, due to the nature of status resistance on shields (shock/fire would do nothing).

I figured that was the point, though - the concept is entirely impractical, but that probably would be the most expensive set (even if it did look absolutely awful!). I'm not sure about you, but I've found that people pay significantly more for fire than other status UVs on shields, with shock/freeze slightly behind that. The UVs wouldn't be practical, of course (*cough* sleep *cough*), but we're just talking about prices.

@Octa, in the darkfang's case sleep would be far more valuable than normal. You can't punch on status UVs for shields, and sleep can't be attained on shields anymore in general. The few that had sleep max on them went for a fortune.

I think the only item people haven't mentioned is a Zee Core.

Zee cores aren't "that" expensive.
Legobuild sold one of his recently to me for 5M cr, his other was sold on the AH a few weeks ago for 2,5M cr.

There was a "Good day for a Knight" contest in which the grand prize was a prismatic party pack - that included a grand topper, unobtainable elsewhere. Would it be more expensive than a darkfang? Unlikely, as if the topper event is ever brought back there's a good chance prismatic would become normally obtainable. Definitely still worth a pretty penny until then, though.