I was never a big fan of the early DS9 uniforms. They just looked too boring and simple-- and even more so on the big screen in Generations (I'm just completely baffled why they chose to incorporate them into that movie).
The later black and gray uniforms still had the same utilitarian feel about them, but also looked a LOT sharper at the same time.
Weren't most of the TNG uniforms showing some wear by that point? Not sure what the deal was with the wardrobe budget but there weren't enough if the new ones to go around.
They spent it on brand-new uniforms that were scrapped not long after filming began (they were kind of a cross between the TNG uniforms, the TWOK uniforms, and the future uniforms in "All Good Things...").