The two UK QRA's - north at Lossiemouth and south at Conningsby - use between 6 and 8 airframes each to keep two at R5 and two more at R30. However, that's the immediate pool, not the deep sevicing, attrition, and training requirements to keep those 6 to 8 aircraft and crews in a condition that would allow to operate the QRA at R5, R30, and R120.
Rough guess? 12+ aircraft to keep 6 at any form of readiness. 20 pilots and 100+ ground crew to get them flying, plus whatever is required to operate an airfield.
Thee one term you'll never used when QRA is being discussed is 'cheap'....