The cost is projected in time road closed (sometimes several hours) which causes cost to businesses, emergency services (fire /police/amb) that have to spend time at the scene (to make safe, deal with casualties and investigate as a crime scene plus a whole load more), some people have extensive hospital treatment before dying( good old NHS....aint free), the protracted investigation which can take in some cases months using scientific expertise...(nope, thats not cheap)...theres a whole load of stuff involved....if magistrates court proceedings take place then that all takes time (public money runs the court system), that can lead to crown court...and of course coroner court...nothings free mate.....and all because someone was stupid enough to get killed eh...
Your views are based on assumption rather than fact....how can you make the system more efficient when you are dealing with someones loss of life? perhaps miss out a couple of things?...there is a whole bigger picture which you are missing