With regards to cost...for the MOD it is not just a unit cost. Hundreds of millions have been paid up front for Hawk 128 development...all in support of UK Plc.
I can't imagine that that any will be painted red with smoke units fitted. Would be a massive underutilisation of the training systems on board. There are enough cheap Hawk T1 airframes to last many many years of swooping and looping.
Raytheon had quoted an extra million per jet to fit a 'modern' radar whilst retaining all the training functionality of the synthetic one. A shame really that this trainer is unable to fulfil a reasonable aggressor or potential AD role. Lets face it, the 100 Sqn Hawk T1A is not really suitable for modern day front-line training.