Hire a venue 4K
Amulance & Fire trucks 2k
Organise proper timing gear that people will believe or a world war starts.
Legal Docs for entrants to sign to stop you going to jail for 50 years in case of a death.
Organise enough cars to cover your costs, an established event like Vmax Charges £145 & gets around 45 cars.
Get any of the million people interested to actually pay money in advance so you dont go broke.

Sorry Dan has replied first hes a faster typer than me.