Assuming generic medium skilled German IT guy's fully burdened cost is $168,000 USD/yr and that this level of effort will require a staffing change (both very good assumptions)
Let's say this medium skilled IT guy gets a €3000/month salary, that's €36,000/year. There will be other costs, but it won't come anywhere near the number you assumed. Also, dealing with malware is a standard task when managing Windows desktop PCs, no matter whether you blame it on market share or on Microsoft. So if it requires a staffing change, then they didn't have the right staff to begin with.
Assume 44 usable weeks a year, or 220 useable days, that's roughly 1 machine a day.
An admin responsible for over 100 desktops should have set up an infrastructure for re-imaging so that it doesn't take 1 day per machine. It's not exactly zero effort like the GP said: you'll still have to warn people that anything they saved on the local hard disk will be lost, for example, but the required effort is in the order of days, not months.
I wonder where that huge cost estimate came from. Did they need justification to buy the new PCs that they wanted for a while but couldn't get the budget for? Was someone really not looking forward to cleaning the PCs and therefore inflated the cost of doing so? Was it just a made-up number that no-one looked at critically? Because it sounds unlikely to me that the actual costs would be that high.