We just build an new office. Just 17 storeys high.
Cost of cabling vs wireless is 50 vs 77 (10 - 15.4) not included tele-mobile servicepoints as on GSM /GPRS /UMTS.
This is CAT6 cabling (tele/data), QoS for using VoIP for satelite offices) and for the conference rooms (25 with total capacity off 1200 guests) teleconference/videoconference/television/radio and so on.
LAN bandwith is 100 mbs from every connecting point.
Extra costs from wifi over cable is more into security of the LAN as anu other costs. This we didn't calculate as it was clear to us that just the trivial cost WIFI would exceed the cost of cabling.

But level of costs do change rather quickly so be alert to cost dropping on WIFI.

Rob