We don't have a posted price list for this page, and giving you a number we can't back up would do you no favors. What we can tell you is what drives the cost on a typical North Branford job: whether it's one spring or a matching pair, torsion versus extension, and whether the cable, drums, or end bearings need replacing alongside it. A double door built around 1977 usually runs two torsion springs sized to match the door weight, and replacing both at once costs more up front but saves you a second trip when the other one lets go a year later, which it usually does once one has failed.
With median household income in the area around $113,687, we see a fair number of owners who'd rather pay once for the full fix than patch one spring and leave a mismatched twenty-year-old spring next to it. That's a reasonable call on a two-spring door, but it's your call, not ours - we'll tell you what we find and let you decide.