go to your local auto recycler (junkyard) and ask them what one costs. should not be too difficult to replace by yourself, but I have never done so on the trep. In any case, a junkyard window will be much cheaper than a dealer, and you might get the recycler for a small fee to put it in for you, or have your mechanic do it.
its really easy to put a new one in, you pull off the door panel which has a couple screws, then lower the window bracket a little till u see the two bolts, just loosen then a little and they slide to the left then up I believe. The new one will lower down onto the tracks sliding it in from the outside, make sure you clear all the broken glass out of the track though, once you get it back on the bracket just tighten the bolts all the way again and make sure its still on the track by lowering and raising it before you put the panel back on..