What LCD said is more or less right. Those are the ranges you'd typically find you will have to pay, but it's important to remember that the rates vary across the country. One thing I always advice others to do is to get quotes from different contractors. It might not be the biggest job, but you'd be surprised how much difference there typically is in the quoted prices. If you check out the link I put in the resource, it'll take you to a site where you can get quotes from 4 different contractors at once. Under "Select service" you simply pick "Spring Replacement".
Hiring a professional to handle garage door spring repair and replacement tends to be a much easier and safer option for homeowners. Removing or repairing garage springs can be a dangerous job, but professionals have the experience and equipment to do it safely and efficiently. Unless your springs only need a minor repair, such as lubrication or fixing a minor balance issue, be sure to call in a local garage door pro to do the job.
Daniel returned my call in ten minutes. It was late in the afternoon and he was at my residence within two hours, arriving half an hour earlier than anticipated. My garage door opener was malfunctioning and the fix was quick and easy. After the repair Daniel lubricated all the garage door springs and joints. Very personable and obviously knowledgeable, he explained everything I needed to do to maintain trouble-free operation of the door. HIGHLY recommend !