Before we begin, I'd like to say that this is not intended to be a guide on how much a specific item is worth. What I intend to accomplish with this post is a general guide on how much an item could be worth with all the circumstances accounted for.
This guide is intended for items that are currently able to drop in game. For any pricing related to items you believe to be pre-nerf, see following posts:
For pre-nerf (unique) items, see this post by Unholy.
For pre-nerf (rare) & (uncommon) weapons, shields and focuses, see Weapons and Shield & Focus by Evelynn Roscoe.
And lastly we have the beautifully compiled General guide by fsc1 for anything else.
- Perfect/imperfects vs. req (Wands, foci and staves)
A 20/20 high req staff/wand/focus is worth substantially more than a q9 20/19, since a 20/19, when equipped, will not have the highest modifier allowed on weapons in game. They're usually called one-offs. They still hold some value to people that really like the skin and won't mind the 1% off, but expect 1-10% of the value a max one would have. 20/20 Q9-10's are the ones holding the big money, but as always, it all depends on what skin.
- Skins
I want to adress a crucial phenomenon when it comes to Staves/wands. Any of these that are a "profession" skin, can ONLY roll HCT/HSR of their respective professions. I.e, a core elementalist staff/wand will only roll elementalist HCT/HCR's (Earth/Fire/Water/Air) while "zone specific" skins can roll into all attributes, excluding FC/SR/ES, thus making zone specific (which I will go into in a second) by far rarer in perfect 20/20 mods.
There is one exception that I'm aware of, and that is core Earth staves. Earth staves in this specific skin (obsidian) are very rare and quite sought after.
"Profession specific skins"
| Core | Canthan | ||
| Earth Magic |   |  |  Obsidian |
| Fire Magic |  |  | |
| Air Magic |   |  | |
| Water Magic |  |  |
| Curses | Blood Magic | Death Magic |
  Evil Eye | Accursed |  Dark Tendril |   Wailing | Bone |
| Domination Magic | Illusion Magic | Inspiration Magic |
  Inscribed | Clairvoyant |    Hypnotic | Jeweled | (Twin serpent) | Jeweled (Metal) | Doesn't Drop in OS |
| Spawning Power | Channelling Magic | Communing | Restoration Magic |
 Restoration |  Channeling |   Communing | Eeire | Doesn't Drop in OS |
| Divine Favor | Healing Prayers | Protection Prayers | Smiting Prayers |
   Divine | Holy | Holy Branch | Doesn't Drop in OS | Doesn't Drop in OS |   Smiting | Winged |
These items are very common and very often roll perfectly into 20/20 of the matching attribute, since there's only 3-4 different HCT's to roll. The only exception again, would be the Obsidian Earth staff. I frequently merch these items because they're hard to sell and there's more of them for sale than people looking to buy. I might try to sell a q9 20/20 one for a couple of ectos, but even then it's a hard sell. Don't expect anything much from these skins. You'll find the occasional player liking the look of the skin and wanting to buy one but that's about it.
Edit: a few of these staves are less likely to drop than other prof specific staves, (thank you Oldschool Cool) see his comment down below for stats from his chest running data.
Disclaimer: This does not include the "profession" wands/foci. Even if they too cannot roll outside of their main profession attributes, having both of the mods on a wand/focus roll into the same attribute is rare enough and will have some interest.
I hope this then makes you realize how insanely rare it is for a wand that is not a profession specific skin to have both mods roll into the same attribute.
Q9 Rare skin focus with perfect matching mods, sold for 300a
added: A few desired mods on wands/foci are a combination of any of following mods;
- 19% or 20% HSR
- 19% or 20% HCT
- 10% HSR
- 10%HCT
- +15/-1 Energy
- +14/-1 Energy
- +1 (20%) mod
- +1 (19%) mod
- And on the rare skins, +5e^enchant
"Zone specific skins"
Now here's where things gets interesting.
These following items are not bound to any specific profession, and can drop for them all. A Bo staff can drop in q9 water and roll a HCT 20% restoration magic. This makes these skins a lot more valuable when they're 20/20 matching HCT's. Since there are so many attributes to roll from, these are naturally rarer than the previously mentioned skins, and harder to obtain in "20/20".
These skins are also valuable when dropped in 20/10 and usually sell for anything around 5-20e.
Restoration, prot and healing staves would be the exception, since they do not drop in OS reqs, and can only be found as HCT's.
Divine favor staves do drop, and are collected in any combination of the monk attributes as well as 20/20 matching.
Example;
A q11 Spawning power Platinum staff with HCT 20% restoration
- Staves, Wands, Foci
Note: Tyrian skins tend to be rarer and more popular.
| Canthan | Tyrian |
 Bo |  Dead |
 Dragon |  Raven |
 Forbidden | |
  Platinum | |
   Plagueborn | |
 Outcast | |
 Cockatrice | |
  Amber | |
  Jade | |
  Celestial | |
 Jellyfish (Wand) |
These three items drops throughout Cantha and are very rare so I decided to include them as well. Any of these will have some kind of value when they're dual modded with max mods. Matching, max, and useful mods? Could be hundreds of arms.
 Paper Fan |  Jug |  Paper Lantern |
Elite zone specific skins
These are the best of the best, rarest and most expensive caster items currently still dropping in game (excluding the Shadow Staff, for some reason FoW items aren't as popular as the rest).
| Urgoz/Deep | Fissure of Woe | The Underworld |
 Wayward Wand |  Shadow Staff |  Ghostly Staff |
 Straw Effigy | ||
 Zodiac Scepter | ||
 Zodiac Staff |
I've always thought of creating this post because of the weekly "what is my q9 blood dark tendril staff worth" posts and the fact that their subsequent answers always contain the word "merch".
I intended to include shields as well but there's just too many variables when it comes to them. Skin/req/mods, max/min mods etc.
I hope I've been able to add something to your price-checking knowledge, and hopefully you'll have a reference point for future questions about skins and their rarities.
Advice for the higher end skins; don't rush the sale. Post it here and try to sell in Kamadan, and make sure to give it some time. There are a lot of collectors that would pay big for these items but aren't active enough to see a selling post that is closed after a week of bidding.
Have fun 
Even rare skins 20/10 often sells higher than common skin 20/20 
