In Complete Arcane there is an item called the "Warlock's Scepter," which provides a boost to eldritch blast based on the number of charges you burn. It requires Bestow Curse to craft. Bestow Curse is 4th level on the Sorcerer/Wizard spell list, so a Dragon Shaman (or a Dragonfire Adept) equivalent should be based around that.
Fittingly enough, Dragon Magic has a 4th level spell called "Curse of the Elemental Lords," which fits both in power level and flavor.
The Warlock's Scepter is caster level 10th and is also a +2 light mace, with a market price of 28000gp.
If we make a spell trigger item (50 charges) at level 10 with Curse of the elemental lords, then apply a 30% discount for being usable by only one class, the market price comes out to be 21000gp. Looks about right.
For the record, burning one charge adds 1d6, 2 charges equal 2d6, 3 charges 3d6 and 5 charges make 4d6. You can't use more than 5 charges at once.
If I come up with more, I'll edit this post.
Edit: Auras increase every five levels, which would boost spellcasting up by two spell levels on a casting class. This part is a little shaky, but I would say the aura boost would be priced similarly to a lesser metamagic rod: empower. 9000gp base, single class discount 6300gp.
As for the natural armor, it's probably easiest to just tack on a natural armor enhancement covered with the single class limitation again (+2 would be 5600gp post-discount).
Having all of this together on one item should invoke the "multiple different powers" price increase, which will nail you with a 50% total price increase. You'll certainly need to check with the DM for an item as convoluted as this.
Total: 49350gp market price, Craft Wondrous item, Sorcerer CL10, Curse of the Elemental Lords
...or something like that. Anyone else have anything to add?