The rank structure of the RAF could be changed.
Maybe (Hahaha) a Flight Commander could be a Flt Lt instead of a Sqn Ldr
or a Squadron Commander could be a Sqn Ldr instead of a Wg Cdr
There could be Group Captains in charge of Groups instead of Air Commodores.
Close bases in the south of the UK where the real workers of the RAF cannot afford a house, and rebuild/reopen bases in the North, and then apply a windfall tax on Annington Homes for the southern MQs.
And Finally to save the biggest amount of money:
The nearest Service establishment to the Houses of Parliament should have a large Premier Inn style block built with 635 rooms. (better still let the MPs live in NORMAL barrack accomodation - then they can live the same way as living-in Service Personnel) All MPs can stay there, and all second homes allowances can be scrapped. No need to pay them extra £400/month for food, as they will be able to get 'home' for food.