At the income level typical for this area, spring repair on a 2001-era door is usually the easy call - the door and track are still in good shape, the spring is a known part, and swapping it costs a fraction of a full door replacement. Where the math shifts is if the opener is also failing or the door itself has started sagging at the panels; at that point, a lot of homeowners here choose to handle the opener and spring together rather than pay for two separate visits down the road.
We can't quote a number without seeing the door - spring size, door weight, and whether one or both springs need replacing all move the price. What we can tell you is that if your springs are original to a 2001 build, they've had over two decades of cycles, and if one has gone, the other is usually close behind on the same shaft.