TCO = Total Cost of Ownership, and refers to the purchase price plus the cost of support over the lifetime of a device, whether it be a computer or a fleet vehicle.
In a survey of corporate IT managers, the Enterprise Desktop Alliance found they responded that Macs were cheaper to manage far more frequently than the reverse (that PCs are cheaper to manage). The survey was divided into six categories, with the results varying from a low of 31% claiming Macs are cheaper vs. 23% claiming PCs are cheaper, with respect to software licensing fees, to a high of 65% claiming Macs are cheaper vs. 16% claiming PCs are, in the case of time spent troubleshooting.
Results in the other four categories fell somewhere in between, with the cost of supporting infrastructure coming in at 37% lower for Mac vs. 25% lower for PCs, system configuration 50% lower for Macs vs. 25% lower for PCs, user training 48% lower for Macs vs. 16% lower for PCs, and help desk calls 54% lower for Macs vs. 16% lower for PCs.
With such a strong indication that Macs really are cheaper to support, it's not so hard to imagine that they might actually have a lower total cost of ownership than PCs.
If you factor in productivity, those "cheap" PCs may be costing you even more.