Because the Wandering Isle is taken apart from the big continents and completely cut off from the original economy, the special economy have developed on the Isle itself.
There are two types of currencies on the Wandering Isle:
1. Gold. Basic currency. With the usage of dailies you can get a fixed amount of gold per day, which can be increased in various ways.
2. Midnight Ink Stack. Secondary currency. There are some items that are worth more than gold, and need more stabile price. That's when Midnight Ink x20 comes into play. It's hard to grind, hard to obtain, and overall is a lot harder to come by then just gold.
I would say one Midnight ink stack is worth around 400g, so one midnight ink is worth 10 gold, BUT the economy may vary on your server depending on the number of stayers and some other factors.
There are some notable items that might be worth a lot of money due to being unique or very rare. The price I'm listing is just theorycrafting, as I've said up it will depend on the number of stayers on your server.
1. Schematic: Mechanical Squirrel Box (http://www.wowhead.com/item=4408/schematic-mechanical-squirrel-box)
Probably the rarest item on the Wandering Isle. The only pet obtainable on the island. Of course to prove you got the schematic or the pet you should keep him in non-learned form in your bags, and show off on trade.
Price: I would say around 20 stacks of Midnight Ink or 10k in pure gold.
2. Glyph of Blurred speed (http://www.wowhead.com/item=43379)
One of the best friends of a Rogue stayer, this little glyph can make your moving across the Island a lot quicker. It allows to run over water when using the sprint ability.
Price: 1.5-2k gold or 3-4 stacks of Midnight Ink
3. Glyph of Long Charge (http://www.wowhead.com/item=43397)
Very very good glyph for a warrior. A few yards will make your moving across the isle slightly quicker, and we all know even a small advantage means a lot.
Price: 500-1k gold or 2 stacks of Midnight Ink
4. Polymorph Glyphs.
Will make your mage's polymorph a little bit fancier. Available variants: Bear Cub, Penguin, Porcupine.
5. Glyph of pickpocket / Glyph of unending Rage
First one increases the range of pick pocket by 5 yards, other one increases your maximum rage by 20. Both with small usefulness, it looks nice to have 120 rage on a warrior.
6. Other Glyphs
All other glyphs available at the isle. For whatever reason you want them.
7. Small Glimmering Shard
For collection purposes only.
<to be continued>
The best equipment on the Island also has its price as follows:
1. Heavy mace of Power / Intellect - 100g
2. Carving Knife of Agility / Power - 80g
3. Infantry Leggings of Power - 50g
4. Hunting Bow - 80g
5. Gypsy Buckler of Blocking - 250g
6. Gypsy Buckler of (X, giving strength/intellect + stamina) - 120g
7. Pioneer Trousers of (Agility/Intellect/Power) - 200g
8. Disciple's Pants of Intellect - 70g
9. Beaded Wraps of Intellect - 80g
10. Short Bastard Sword of Power - 220g
11. Imbued Pioneer Belt - 125g
12. Study Quarterstaff (of Intellect / Power) - 500+g. (Very rare, would loot only from Vordraka, if seen with these modifiers take immediatelly. small note - only green staff on the isle)