This is very difficult to price. Rather than do it based on spell level, lets work through the effects.
DR/adamantine is among the best in the game, since few things penetrate it naturally and it is very expensive.
Other DR granting items to compare to:
Mantle of Faith (DMG) DR 5/evil, 76k
Shirt of Angels (MIC) DR 3/evil, 15k
Shirt of the Moon (MIC) DR 3/silver, 15k
So first, clearly the cost of DR has changed from the DMG to the MIC. So, assuming the MIC is better, we need to increase the base cost of the DR, since it's a better type, and increase it by a factor of five. If we say that DR 3/adamantine costs 20k, and x5 effect is x25 cost (by the standard DnD theory of bonus squaring), that's 500k.
Basing it off of the mantle produces 900k.
The next effect is a necklace of adaptation (9k), a periapt of proof against poison (27k), heavy fortification (35k or more), plus immunities to blindness, ability damage, immunity to electricity (>44k), stunning, and half damage from fire and acid. The mind boggles at trying to price these effects. The electricity immunity does come with the slowing effect as a drawback, but the package is still worth over 100k, easily.
Now, the ability modifiers. +6 Strength, -6 Dex. Not worth that much, comparatively. Obviously less than 36k, lets call it 15k.
Half speed sucks, armor check and ASF suck, but not so much. No potions is mildly annoying, no wind instruments is negligible. Slam attacks, at this point, does it matter? We're estimating so wildly...
I'd call it 650k.
That's without enlarge person.
The point is, so frikkin expensive that gp value is the wrong measure. This item can't be bought or sold except in a game so epic that you are using other rules which you (hopefully) have enough experience with to make it work, since core DnD is no longer helpful.
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gnfnrf