Meh. AC is useless at higher levels. I wouldn't worry much about it as more than a token defense, really.
Get a couple of (relatively cheap) wands of Extended blacklight, and a 2000 gp Ring of the Darkhidden (from the MIC). You're permanently invisible to darkvision, and barring true seeing, that's the only way to see in a blacklight. That's 50% miss chance and inability to be targeted right there.
Getting a wand of mirror image and the blur enhancement on your armor (see MIC again) will give you stackable miss chances, as well; while blur won't stack with the blacklight/ring combo, mirror image does...kind of. The blacklight will affect all of your images, which don't all have to be in your space, meaning that they'll confuse the issue as to which space you're in. And if the cantrip is dispelled or negated, you still have a lot of images to use as decoys.
There's also blink and greater blink. They certainly don't stack, but that doesn't mean you can't use them both at different times. They do, however, stack with all of the other miss chances mentioned, and true seeing won't do much of anything without access to a ghost touch weapon.
There's also silent image and similar spells; create an illusion of a solid wall, and you can jump in and out of it to grant yourself concealment. Also helps when trying to Hide and effectively become invisible. Great for utility, too.
Also, there's Leomund's tiny hut; so long as you're willing to do some sniping, it should help considerably for keeping you out of sight (but not out of mind).
Obscuring mist, smokesticks and such are good ones as well, so long as you've got a way to pierce the concealment. I suggest some way to get touchsight.
You can always use a bullseye lantern and a pyrotechnics spell to blind enemies (and the lantern means there's no chance of blinding your party). Darkstalker is a great feat to add, as well.
The Cloak Dance feat (XPH) will let you (essentially) get a version of Hide in Plain Sight, if you have a decent Hide score. All you need is a cloak and the prereqs for the feat.
Speaking of the XPH, check out the concealing amorpha and greater concealing amorpha powers. They aren't pierced by true seeing, though I'm not sure about how it interacts with touchsight.
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As far as ACTUAL AC bonuses go, stock up on small AC bonuses. Six +1s will be considerably cheaper than one +6. Armor, shield, natural armor, deflection, dodge, insight, morale, exalted, vile, and as many untyped bonuses as you can get. Psionics is good for several of them, and take a few levels in factotum and a few instances of Font of Inspiration if you've got a good Int score (as it's a cheap and easy way to get rather sizable bonuses to your saves, AC, and attack and damage rolls). You also get bumps to your skill monkey pursuits. Best of all, it costs no money and gives you more than just AC bonuses. Does cost some levels and feats, however.