Costs are probably negotiated but per 1,000 employees, most businesses will be paying somewhere between £500,000 and £1,500,000 each year just for Microsoft 365. So I'd estimate the UK civil service at a similar sum £45-500m per year for desktop services. Thats before any Azure or AWS costs

For 27 EU member states, an assumption of €10B / year leaving the EU and going into the us tech giant economy doesnt seem crazy.

So the scare tactic €115b is over 5-6 years. While it would take 10-12 years to save that from fees paid by the central government services alone. Thats a 50% offset immediately on top of the advantages of keeping those vast sums within the EU economic zone. I reckon local authorities and other public services across the wider public sector could offset the other 50%