Who makes the jacket? Some manufacturers offer inexpensive repairs on gear--we've had good experiences with Western Mountaineering and Big Agnes, but I've heard that a lot of the other "big names" have similar policies.
Also, what is the failure? If it's just that the slider doesn't zip the teeth together but the zipper teeth and backing material are otherwise OK (no missing teeth, etc.), you could try:
1) Gently squeeze the slider with a pair of pliers. This is at best a temporary field repair.
2) Amazon has inexpensive ($10) screw-on replacement zippers (Fix N Zip) that allow installing a new slider w/o having to do any stitching. The main downside is the old slider will still be installed.
3) A local shop that does tailoring/clothing repairs should be able to replace the slider, or you can even do this yourself with some hand stitching.