Re: Who is going to pay for all this?
I am confused as to why anyone thinks the UK will need to pay for any such border controls for goods post-Brexit. Unless we are complete idiots and decide to make things more expensive for ourselves for no good reason, that is.
Right now stuff can go from the Republic of Ireland into Northern Ireland without having to pay customs charges. Why would we want to change that? Why would we arbitrarily make it more expensive for ourselves to get hold of these goods by taxing ourselves on them?
Now, if the E.U. demands that the Republic of Ireland place an import duty on goods crossing the other way, that is a different matter and, of course, their decision to make. And one would imagine the Republic of Ireland would be looking at getting some extra cash from Brussels to help pay for all that. Or they would all collectively decide not to bother, or declare that it's happening but never actually do it, which is a pretty common political fudge.
Demanding a border at which to apply something like their 30% tariff on Cocoa Powder is the E.U.'s problem, not that of the UK. If your neighbour decides to pour rocks into their harbour to obstruct incoming trade vessels, you do not make yourself richer by also pouring rocks into your own harbour.