Do a little bit of detective work before deciding it is the starter.. especially if you notice other problems in the ignition system.. like a falty key switch.
Try another battery.. perhaps one out of your car/truck, and see how it turns over. If you have a hygrometer.. test your battery cells. Also.. many places also offer free battery testing.
Try jumpering around your key switch.. or even jumpering right from the battery to the starter to bypass the solenoid. Might be a 1$ wire or a 15$ solenoid, or a 10$ switch or a 40$ battery, and not a couple hundred dollar starter motor.
Soundguy