<p>How do I determine how much an individual print costs?</p>

<p>I'd like an answer including support material, failed prints, and (ideally) wear and tear / printer maintenance costs.</p>

<p>To clarify, I'm not asking how to <em>predict</em> the cost before printing, but rather how to calculate the actual cost after printing. Though predicting the cost beforehand is useful as well.</p>

For
FDM
printing:
Both Cura and Makerbot Desktop (and perhaps others I'm not as familiar with) will give you a preview of both the length and weight of your print, including supports/rafts. Once the print is done you can weigh it on a kitchen scale.
PLA Filament currently runs about \$23/kg on Amazon, which works out to \$0.023/g. Multiplication can then give you a good estimate of materials costs for a print.
Only experience with your specific printer will give you an idea of how often you're going to hit a failed print, and how often you're going to need to replace parts. For wear and tear you could try using a depreciation model of 2-3 years, but that's only an estimate.