"British businesses face an “administrative burden” cost of £7.5bn a year in filling out customs paperwork after the Brexit transition period, the chief executive of HMRC has said."
So basically about the same amount that we pay into the EU, but without the returning investment amounts...
Loss of trade/tariffs/loss of influence will cost tens of billions more, and of course there is the social costs...
Brexiteers sure know how to organise the worst p*ss up in history!