It is not difficult to bypass the stater switch, or the the starter switch and the solenoid. It is just a matter of jumping some connections at the solenoid, on the motor.
It is very worthwhile to know how to do this.
To bypass the starter switch. Jump the main positive lead ( the thick lead with a wire to the battery) and the ignition switch lead ( which will be a much smaller stud and wire) . This can be done with a screwdriver. It is even worth considering installing a permanent switch to do this.
To bypass the solenoid jump the two heavy wires on solenoid. (Note this is a lot of current
sparks will fly). Be careful not to touch the case or any other metal. This will spin the starter motor, but with the most common type of preengaged starter will not start the engine as the solenoid is needed to engage the starter on the flywheel.
If you get someone to hold the ignition switch at the same time the starter will engage and the engine will start ( if the failure is due to the solenoid contacts which is most likely)
These steps are very likely to start the engine. They also diagnose where the problem is. If not, you know the problem is not with the starter switch or solenoid and can look for other possibilities.
In the photo
you can see the smaller solenoid which is on top of. The starter motor. The two big connectors (one with a wire leading to the starter motor and the much smaller connector is connected to the ignition switch.