If you look in the dictionary, one of the explanatory quotes is "..the coal mines were subsidised."
As we no longer have a mining industry there is no subsidy. This is like accommodation ashore. A level of rent is set and the occupant pays it. There is no mention of subsidy, just a payment for the accommodation. And the occupants don't have to work in the coal mines. If you live onboard there may be single cabins up to dormitory style and everything in between. This depends on base, rank, job etc. Also orficers may have "better" accommodation than those below him/her. There is no simple answer.
At Raleigh you will be in a 20+ Man mess.
For phase 2 it will either be; Sultan 16 Man mess, Collingwood 6 Man mess with bathroom and kitchen.
Nelson 2 Man shared cabin for AB's, Can't comment on Devonport or Faslane, as I have never been fortunate to stay there.
Cost will vary on standard of accommodation. anything from £30 per month to £70 for JR's.