The $10,000 for the Windows OS on a volume license is just the start of your Windows related costs. For volume licensing, you will need Microsoft file servers, license servers, and an abundant number of other servers, all of which will need licenses from Microsoft. You will also spend a significant number of staff-hours per week maintaining that software, which is significantly more vulnerable to attacks than a proper Ubuntu-based network.
Also, the cost for 'inventory, warehousing, offices, consultants, and contractors' previously cited may not pertain to your business model. By all means, do budget for those if you must have them, but I won't speculate on what you will or won't need in whatever your line of work will be. I will, however, expect the cost of operating and maintaining an Ubuntu-based network will be even greater a savings than the savings from a free OS and free applications.