I know that when I was in from 2003-2007, I didn't have to pay anything to go from BDUs to DCUs, as I received a one-time uniform stipend of a couple hundred bucks. Purchased two sets of uniforms, as I recall and pocketed the rest. And that was with me being in garrison and not scheduled to be deployed anywhere.
Come to think of it, I think the only "essential" uniform item I purchased during my time on active duty was a pair of black jungle boots, but that was just so I could get out of those awful leather boots they issued me in basic.