how about electricity cost? it is also cost of doing business as far as mining concerned right? And in the US it aint no cheap!
Electricity costs are a full deduction, so make sure to keep track of how much power you are using and record it. We record power usage daily using killawatt meters on each rig and a spreadsheet. That way if we're ever audited we have proof to show them. It's also helpful for seeing exactly how much power you're using when mining different algorithms etc...