how much does 1 qubic inch of printing material cost?
That varys from material type to print size. If i do a large print like a helmet, that can be as much as 50 dollars worth of printing material. It also depends on infill. if i'm doing 100% infill it can be very expensive.
On average, when printing say a 2x2 lego you're spending out 19 cents of printing material from a 1lbs spool
If you're going to do 3d printing, do what treynolds said and avoid FDM printers. They're mostly hype and expensive to maintain.