Single-Role - Multi-Role
Single role would certainly be less expensive airframe for airframe but then risk having numbers of the wrong airframe that were unuseable is a given scenario - Jaguars inb AFG might be a case in point.
A multi-role aircraft could mean lugging around unnecessary equipment for a particular role - sonics on SAR or ASR on ASW etc.
Several single role types requires more bases - Cottesmore - Wittering-Coltishall - which increases the aircraft operating costs etc,
A large multi-role base - Marham-Kinloss - may be less expensive but the more complex systes require more maintenance - Nimrod had its cameras removed to save servicing costs and aircrew need more training to reach the same multi-role capability as single-role types.
For the latter reason the original Typhoon concept was for two single-role types and one swing role.
It really is a slide rule issue and not a fag packet one.