Love my old model 12 (1912). Depending on what the issue is, you might be able to just purchase the new firing pin and replace it. Generally there is a retaining screw that needs to be removed so that you can remove the firing pin. Order a new one, drop it in place, replace the retaining screw, and start shooting again.
Some retaining screws are staked (hit with a center punch on the edge) to keep them in place, so the use of the proper screwdriver bit is important.
If that is all it is, you should be good to go, and it should not cost $400.
Is there a local skeet or trap range where you are at? Try there when they have a large competition, as a lot of trap guys shoot model 12's, and there would likely be someone there who would have aftermarket parts.
Some retaining screws are staked (hit with a center punch on the edge) to keep them in place, so the use of the proper screwdriver bit is important.
If that is all it is, you should be good to go, and it should not cost $400.
Is there a local skeet or trap range where you are at? Try there when they have a large competition, as a lot of trap guys shoot model 12's, and there would likely be someone there who would have aftermarket parts.