my car is cranking but not starting, my friend suggests that it could be that the coil is shot... could that be a cause of my problem? if so... how much would it cost for a new coil and is it a hard installation

 

First pull a plug wire and make sure you are or are not getting a spark at the plug.
If you have a distributer type ignition (5.0) it could be the ignition module. 4.6 engines can have crank sensors or cam sensors go bad.Loose wires can cause the same problems.