Built-in and over-the-range microwave repair in Sacramento typically costs $150 to $400. Door-switch replacement — the most common microwave failure — runs $150 to $250 including labor. Line-fuse, thermal-fuse, and turntable-motor replacement fall in the same range. High-voltage diode and magnetron replacement typically runs $250 to $450 depending on model.
Countertop microwaves are a different economic calculation. The repair path and parts are similar, but a $200 repair on a $150 countertop unit rarely pencils out. For countertop microwaves, repair usually only makes sense when the part is cheap and the unit is premium — a built-in countertop convection microwave can justify a repair that a basic unit can't.
Over-the-range and built-in microwaves are the opposite. A GE Advantium, Wolf built-in, Bosch 800 Series, or KitchenAid convection microwave is a $900 to $2,500 appliance, and a $400 magnetron replacement keeps the unit running for years. Built-in and trim-kit units are also non-trivial to replace — the replacement unit has to match the existing opening or the cabinetry needs to be modified.
If the microwave is sparking inside the cavity, stop using it immediately — that's usually a failed waveguide cover or a burned spot on the cavity interior, both of which are fire risks.