in all likelyhood it might be just the starter solenoid
but here recently i had learned a valuable lesson about that
so as edward mentioned , please do check the voltage from the start circuit and make sure you do not have any other high resistance points such as bad keyswitch or neutral start switch or even bad wiring in the start circuit. My experience wound up being some bad connections at the neutral safety switch which lead me around in circles after 2 starters and a battery cable end replacement. I was getting an intermittant voltage drop in the circuit that caused the starter to seem to fail (the perverbial clicking). I replaced the connectors on the wires at the neutral safety switch and the truck has started flawlessly ever since.

so......
- load test the battery to make sure its good
- make certain there are no bad conncections anywhere in the circuit
if in the end it winds up being a bad starter solenoid then by all means go have it rebuilt or install a reman aftermarket one if one is available.

good luck :o)