I have a 98 Subaru Forester. I think I need a new master cylinder. Does anyone know how much that repair is?

If you buy the part through napa it is 36 dollars with a 17 dollar core, remanufactured.

The labor for the install would be 2 to 2.5 hours plus brake fluid. May be more by the book but you have to bench bleed the master and bleed all 4 brakes when you install it. Its just two 12 millimeter bolts, 2 10 millimeter brake lines, a level sensor and a pin holding it in.

Most garages mark up the parts so expect to pay more if you have a mechanic do it.

Why do you think you need a new master cylinder? (You did not say.)

If it appears to be low on fluid, but is not showing any signs of leaking, it may be that you actually need replacement brake pads.