The BBMF aircraft are not owned by the RAF or MOD but leased to them, so the costs there can be if need be passed back to their owners.
As for the Vulcan whilst it would be amazing to see it flying again I don't see how we can expect the HLF to keep dipping into the pot. THat said though some of the projects they and other lottery agencies have paid out have been diabolical. 50m for the opera house in London for example comes to mind.
How many aviation enthusiasts are there? Why can't we all dip in to our pockets and donate a tenner each I am sure that would be a big step towards the 250k
Rob