prOOne and JN are quite right: the contract is designed to stop the Germans walking away in the early 90s when they were going broke integrating the former East Germany. This lead to the contemporaneous rebranding of the programme as Eurofighter 2000, which IIRC, was made cheaper for the Germans by reducing the spec of their EW fit amongst other things.
So, what do we do? To keep the jet in service through to OSD will require 232 for a 7 Sqn frontline.
Q1. Can we reduce the buy?
A1. Sure, by reducing the number of frontline Sqns or bringing forward the OSD. Is this sensible? No, probably not.
Q2. Can we spend less money in the next five years when the EP is maxed out?
A2. Certainly, by flogging the jet to other countries and coming back to the UK buy later on. Does this save money in the long run? No, probably not, but it may get us more T3 jets than we would otherwise have ended up with.
The real question is whether the Saudi and other export jets are counted against the UK's 232 - and if someone out there in Ppruneland can provide the definitive answer, that'd be great.
S41