You can bypass the solenoid on the starter by taking a screwdriver or wire and shorting the two main terminals on the solenoid. Have someone else sit in the truck with the ignition on, trans in neutral, clutch pressed in while you do it. If it starts, it's the solenoid on the starter.
FWIW, a new starter comes with a new solenoid and probably wouldn't be much more expensive. I just replaced the starter on my girlfriend's mother's Bronco and it had the same symptoms you have. I didn't wven bother testing the solenoid because a brand new starter was only about $50 more, the old starter was likely the original and may have failed soon after anyway, and the parts store only had the starter in stock, not the seperate solenoid.