The St. Louis Post-Dispatch has this sales receipt for the vest used by James Holmes. If you go to Tactical Gear, you will see that while this is an "assault vest," it is hardly bullet resistant. The vest is apparently an "assault vest" because it has pockets to hold multiple magazines. Here is the description provided of the product (click on the picture to enlarge). Nylon isn't going to provide much protection against bullets.
Tactical Gear does sell bullet resistant vests, but they are much more expensive and are in the $500 to $620 range. Of course, even if it had been a bullet resistant vest, it is still possible for bullets to penetrate, and in any case hits on the vest would have likely knocked him down and stopped the attack.
Note that in July the New York Times mentioned this Blackhawk Urban Assault Vest, but apparently they had no idea what they had.
In early July, Mr. Holmes ordered a Blackhawk Urban Assault Vest, a knife and two magazine holders from a Web site called Tactical Gear, according to an order slip provided by the company’s chief executive, Chad Weinman. He chose expedited two-day delivery to his apartment in the eastern Denver suburb of Aurora, where the shootings took place early Friday, just a few miles from Mr. Holmes’s apartment. . . .
Yet, the same article noted: "He also bought bulletproof vests and other tactical gear . . . ."
Thanks very much to Lon Williams for these links.