if you buy the motor/regulator from a salvage yard, you should expect to pay about $75 for it. your avarage shade tree mechanic can swap it out in about 1.5 - 2 hours. its quite easy. im not sure what the labor manual gives as a labor time for a garage, but a decent mechanic will have that done in less than an hour. figure $50- $100 for labor if you have a shop do it.
or, do it yourself. once you have the door panel off, theres 2 bolts that hold the regulator to the glass, and about 6 bolts that hold the regulator to the door. an electrical plug, and thats it. easy.