The power locks on your car should last as long as the car Since your car is relatively recent, I'd do as Steve R Jones says and hit the junk yards. You'll save one heck of a lot of money and these parts should be in great shape from any front or rear collision. Keep in mind that you need the Motor, Window Regulator, Inner Door Panel, Wiring Harness and Switches. It's a little more involved than most people think.
You could also check out J.C. Whitney for possible after market parts. They may sell kits for your car/model.
what edhe62 said. unless you get that kit to work, theres nothing easier than ripping a set off a junker at the yard and easily installing it into all of the pre-drilled holes already ready for you.
but, my 99 ranger is only 6 years old and the power lock dont work most of the time, but ive also seen them work for ever. You probably have an electric motor kit, while many power locks work off vaccuum. i think a vacuum motor will last longer, plus you get to use the lock once or twice while the engine isnt running, but if the lines arent already there it isnt worth the hassle. For $17 i wouldnt worry about durability, even if you replace them every 3-5 years big deal eh?