Flying anorak
A military size order for the Rotax 912/Grob 109 would undoubtedly give the retrofit program a boost in terms of economy of scale and is the only game in town for the continued operation of a Grob 109 fleet of any size. However the biggest slice of the cost is the engine so I don't see much change in the £30k cost.
All is now being done ( within the ability of the industry ) to get the air cadet gliders back into service, motor gliders will come later.
I look forward to the day in the near future that ATC cadets will be once again enjoying gliding as I did far too long ago !