You technically aren't wrong.

But, in my case, I already had all of the capacity paid for regardless. I'd say, lemmy runs me around 20-30w of load total.

30w * 24 hours * 30 days = 21,600Wh / 1,000 = 21Kwh * 0.08c = 1.68$ per month.

In reality, the power load is quite a bit less, and my calculations don't account for the solar panels on my roof.

Given, I have around 140-160T of total storage capacity, its not really worth putting a price on the small amount used by lemmy. My internet is paid regardless, and lemmy usage is typically pretty low (typically measured in Kb/s). So, not really worth putting a price here, as it averages less then 1% of my total connection.

If, I wanted to put a price tag on it, my labor to actually support and maintain it, would be where all of the money went to.

Contabo's sign up page lets you pay for up to 12 months at a time, in advance. It's quite possible they paid for a year, set it up, and then forgot about it or haven't been able to administer it for other reasons.

As if everyone running a home server has proper monitoring. You think running an instance is going to make a noticeable difference on your electric bill? Mortgage for the server?