Do you hear the starter solenoid clicking when the key is turned? If you hear it click but the starter doesn't engage, the problem is most likely the starter contacts.
If it doesn't click, check for voltage on the small wire at the starter end. If it is getting voltage, the starter solenoid is probanbly the problem. In that case you may be facing a starter rebuild or replacement.
If there is no voltage, the problem could be in the ignition switch.
I haven't had any trouble with my truck yet but when my 90' chrysler wouldn't start I finally found that the ignition switch was broken. In fact it was the lock cylinder that broke. I could turn the switch on and everything worked OK but when I turned it to the start position, nothing happened.
There is a protrusion on the end of the lock cylinder that rotates the switch the last part of a turn to engage the starter.
The protrusion was broken and the lock had to be replaced. A new lock is in the $75 range but on some of them, parts can replaced.
When the lock has to be replaced, they will pin it for your original key.
I haven't seen anything like this mentioned on the forum before so thought I would throw it in as another possibility.
The Dodge and Chrysler locks both look alike so I would guess they are pretty much the same. Probably even interchangeable.
Attention: TDR Forum Junkies 
Lately I’ve been having intermittent problems starting my ’96 Ram w/ automatic transmission. When I turn the key, nothing happens. I have power to the truck, no power drain (at least no more than normal), just no cranking. Sometimes I have to turn the key to the “off” position and back to the “on” position several times before it begins to crank & start. My local mechanic couldn't find the problem because the problem couldn't be reproduced by him--- (ain't that always the way?). So, anyone have any ideas? 
Actually, when I turn the key, nothing happens. No clicking, no nothin'. Though, one time, I did hear the starter continue to run for a short while after the engine started.
