Wreckfest

Some cars will unlock throughout the game by completing certain events, others you will have to buy. The special vehicles are the ones you unlock by completing challenges:

Lawnmower (Eat Dirt! Challenge)
Sofa Car (Couch Craze Challenge)
School Bus (Oval Challenge – Destroy All Supervans!)
Harvester (Harvesters From Hell Challenge)
Double Decker (Double Trouble Challenge)
Supervan (The Great Escape Challenge)
Limo (Limousine Demolition Challenge)
Motorhome (Motorhome Madness Challenge)
Semi Truck (The Convoy Challenge)

In the end it doesn't matter whether you own special vehicles or normal vehicles, they all count towards the trophy. You will earn plenty of credits while going for the other trophies to buy enough vehicles.