Re: $100 per seat per year
Don't forget that this is a 'cloud' implementation - outright purchase of Office would cost a large government agency around $30 a seat, the extra is going to pay for storage and CPU power on the MS cloud. If you want to compare equivalent costs with OO, you need to include a contract with Amazon, Google or someone for those resources (I've little idea what that would be as I have no interest in the proposition, but a few $ a month a seat might well cover it).
You may be right about those who would be inconvenienced, but if one of the 1 in 20 is a CxO (or their PA) you may be heading for a world of pain. And you might be surprised how many organisations use Office macros, which don't migrate easily to OO - collection/validation of monthly financials from first-line supervisors is a good one.