Warforged are actually somewhere along the lines of 500+ for the low-end models (as stated in one of Keith Baker's mammoth Q&A threads on the WoTC boards, which I'll dig up if I find more time to waste): Cannith used the Creation Forges (aka. artifact-level plot devices), which not only speeds up the creation process, but also reduces the materials (and supplies most of the XP, presumably) needed to create them. Expensive/rare metals such as Mithril or Adamantine are not actually used, but are rather 'created' through the use of the Mark of Making and sustained afterwards by the Warforged itself. Removing the metals from a Warforged's body results in rapid decay. Therefore, it's not really that expensive to make one.
Details can be found
here.
Disguise might be a Cha-linked ability, but it's a meer -1 penalty. You can easily compensate with a Potion of Disguise Self, or even a Hat of Disguise for a +9 bonus. For Bluff, the same can be solved with a Potion of Glibness. Warforged infiltrators don't stick around, they go in, grab the target, and get out quickly, so short term buffs are acceptable. Alternatively, don't be seen at all with Invisibility and/or Silence: measures like See Invsibility and Invisibility Purge both have range limitations, and are further hampered by the fact that they still have to be active at the right time (unreliable), or all the time (expensive). Meanwhile, an infiltrator can use diversions to turn attention away at an opportune moment, find a way to disable such protections, or even find an alternate route in: not needing to breathe and a immunity to nausea/sickness/disease can open a surprising number of routes *coughprivysewercough*.
Long term infiltration is a much more specialized job requiring significant resources to dodge the nigh-omnipresent magical measures: a job left to specialists such as House Philarlan and Thuranni, who have perfected their craft since the Age of Giants.
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