When cars die (or in this case limos) they usually leave behind a ghost - esspecialy if they had a gruesome death. Ghost limos are exceedingly cheap, due to their inabillity to drive at fast speeds (you know, because of their mangled bodies). This is one of the reasons Hogwash bought so many of them. That and because everyone was tired of stepping in invisable thestral poop. The ones at Hogwash only go about thirteen miles an hour.
At the start of Barry's fifth year he intentionally missed the Hogwash Express and made plans to travel to the school via a paper umbrella with a Homing Spell on it. Once his umbrella craped out Hafwid arrived in a french maids outfit (the only muddle clothing that fit him) and whisked him away in a ghost limo.