$20 - $30 is about 10X too high. Electronic parts stores have these for $2-$3. The tricky part is the small moving actuator tab, which may be unique to Volvo. You may have to either transfer the actuator to the new switch, or bend a generic one.

The switches are located along the outer rail (the side where the controls are located). They limit the maximum travel of the seat. There are two for each seat, to limit the fore and aft travel.

Usually, the most expedient way to repair a power seat is to remove it first (four bolts and some connectors). I doubt if you can access the microswitches otherwise.

There is a control computer mounted to the underside of the seat. Perhaps that is what they are replacing for $250.