Is there a difference between the cheaper car chargers and the ones from the actual manufacturer (referred to as OEM, such as Motorola, Kyocera, Nokia, Samsung, etc.) ?

There certainly can be. Many of the cheaper ones either are made with inferior materials and/or don't meet OEM standards. Some cheaper ones may not even have a "voltage regulator" built into them to prevent damage to your cellphone battery or cellphone itself ! Generally, there is no "free lunch" so if something is much less in price than its competitors, it may not be worth the risk to buy it.  You probably shouldn't risk your $200-400 phone with a cheap poorly made car charger. That's not to say you can't find a good deal here and there but just be aware that some things are cheap for a reason.

Hope this info helps you become better informed for your purchases.