I use $1 USD per watt per year, with electric prices around $0.10/kWh. Good enough to inform decisions like whether to leave a light on all the time ($5/year) or whether to purchase a NAS vs. used server ($40 vs. $300 per year).

I guess my prices are actually a little over $0.10 and a watt over a year is a little under 10,000Wh as shown in your calculations, so those offset to make the estimate even more accurate (than necessary).