Numbers first, because that is what you came for. A single torsion spring fitted runs an estimated $185 to $340. A matched pair on a double door is an estimated $265 to $470. The long extension springs that sit beside the tracks on older doors are an estimated $155 to $260 for the pair. Every one of those is a guide band and not a quote, since the price turns on the door weight, the spring size and what else on the shaft has corroded. What follows is where the money in those bands actually goes.
You are not paying for the coil
A standard torsion spring is a length of wound hardened wire and it is one of the cheaper items on the whole door. The invoice is built from what happens either side of fitting it. Reading the old spring, weighing or calculating the door, matching the replacement, then winding it in quarter turns with two proper bars while the door sits clamped in its track. Add a van that carries spring stock in a spread of sizes, because nobody drives back across town mid job to fetch one. Skilled time and having the right part on board is most of what you are buying.
Sizing is the part that goes wrong
A spring is defined by four things: wire diameter, inside diameter, overall length and wind direction. Miss any of them and the door is out of balance from its first trip. Underspecified and it feels heavy, sags near the top of travel and leans on the opener for the difference. Overspecified and it fights back at the floor, the door floats up off the slab, the reverse function gets confused and the top section carries stress it was never built for. DASMA publishes the data that matches a spring to a real door weight, and a proper fitter measures instead of eyeballing. This is how a bargain online spring kit ends up as the expensive option: the part, then a call-out to undo what the part did.
Two springs on the shaft, one broken, both replaced
Most double doors carry two springs either side of a center bracket. When one lets go the survivor is not a fresh part, it is the next one, because it has done the same number of trips in the same air on the same shaft. Fit one and you pay the labor twice, often inside a year, and run a door that lifts unevenly in between. A few blocks from the water the argument gets stronger, since both coils have spent the same damp mornings collecting the same surface pitting. The pair at an estimated $265 to $470 against a single at an estimated $185 to $340 means the second spring costs a fraction as part of one visit compared with being a whole visit of its own.
Coated wire, roughly 10 to 20 percent, and why it earns it
Ask about galvanised or coated spring wire before the job is booked. It adds roughly 10 to 20 percent to the parts line. Within about a mile of the sand that is the best value on the invoice, and here is the mechanism. On bare wire there is a narrow band along the inside of every coil where the metal almost touches itself. Damp settles in that gap, dries slowly, and the coil starts to bloom with fine rust. Coating keeps that seam dry for years longer, which pushes a coastal spring back toward an inland lifespan. Head east of Interstate 5 and the case weakens. By Bonsall or Fallbrook it is money you do not need to spend. Distance from the water decides it, not the size of the door.
Cost per year of service beats cost per spring
Springs are rated in openings, not birthdays, and a standard one is wound for around 10,000 cycles. A household running the door four times a day gets through that in roughly seven years, so a pair at the middle of the band works out near fifty dollars a year of service. Put the same spring on a short-term let near the Pier where guests, cleaners and an owner all come and go, and the rating is spent in about three. That is the point at which a high cycle spring rated 20,000 or more looks cheap despite the higher parts price, because the second visit never happens. Cheapest today and cheapest across ten years are two different questions, and only one of them shows up on the quote.
What a fair quote mentions alongside the spring
Ask up front what gets inspected while the shaft is being turned. The shaft itself gets checked for scoring under the drums, both end bearings and the center bearing get spun by hand, the drum grooves get looked at, and the lift cables get examined. A corroded cable bolted next to a brand new spring is simply the next call-out with a date on it. Cables run an estimated $135 to $245 the pair, drums and bearings an estimated $130 to $250. In Oceanside CA an honest quote often carries one of those, and it costs less inside the same visit than as a return trip. What should never appear is a firm figure over the phone before anyone has seen the door.