Start with the price you actually paid
Use the delivered price per kilogram for the pack you bought. A discount that requires five reels is a different offer from a single spool, and a refill may require a separate reusable spool.
Count all the material once
Add up material consumed by successful parts, failed pieces and waste. If you have already measured total consumption, do not add the waste a second time. Slicer figures are useful estimates, but label them as estimates rather than measured use.
A worked example
Suppose a £20/kg filament uses 100 g across two usable parts and the waste from those attempts. Material costs £2. If the printer uses 0.5 kWh at £0.30/kWh, electricity adds £0.15. The total is £2.15, or about £1.08 per usable part.
Those are example figures, not a result for a named product. You can replace them in the print-cost calculator.
What the calculation leaves out
Printer purchase, maintenance and your time are not included in the basic material-and-electricity figure. They matter for a business quote, but mixing them into a simple filament comparison without explanation makes the result harder to use.
Keep drying and calibration costs separate, then include them when they belong to the question you are answering. A first-use cost with calibration is not the same as the cost of the next routine print.