Interesting project.
I think energy costs remain one of the most important variables in mining profitability.
In addition to electricity prices, I also monitor network difficulty, fee market activity, and mempool congestion because they can significantly affect miner revenue.
Solo mining devices consume very little electricity, so you won't notice a significant increase in expenses from a small 300-watt unit running in your apartment. At US rates,
220 kilowatt-hours per month costs around $50–$60, which isn't much. In other countries, it would be even cheaper, for me, it costs $13.