FYI a 48'-53' truck is a Semi... and will require a class A license to operate. So renting it is out of the question.
If you have a solid truckload 18 pallets is about a truckload... and the driver doesn't have to load the trailer. You can call just about any trucking company and negotiate a rate or check out iship.com.
If the pallets aren't ready for prime time, meaning they can't just be loaded from a dock. You'll need a mover, or you could palletize the stuff and then call a trucking company.
They usually charge by the mile, $10-$18 per mile is pretty reasonable, but probably be more. You can get a flat fee off iship.com but not all drivers there are professionals and carry the proper insurance.
Hope that helps..