I'd rather just see the kwh usage. Rates vary wildly in the US, even within the same state. Some states with average prices have utilities with cheap power.
And others with overall low rates have dumb utilities that charge high rates if you use more than 1000kwh, which most EV owners certainly do.
Yes rates vary, the point is to have ballpark figures to compare against the cost of gasoline. Without that the conversation is not particularly useful.
If we know the kwh, we can extrapolate both that and situation specific numbers. Average $/kwh in the US is ~$.15.
This is just like a gas car, where the conversation would start with mpg, not "What's your gas cost per month before and after getting gas car?" It is precisely because of the variation in both gas price and usage that it is important to start from consumption per mile and not a total price.
Asking a random person for their kwh usage is not realistic. Dollars per month change (where they haven't changed driving drastically) is more practical.
But you aren't asking random people. You are asking EV owners on Hacker News.
In general, EV owners are pretty savvy. More than most actually know what they pay per kwh and have a pretty good idea of their consumption. The biggest common mistake that I see is net vs gross.
And others with overall low rates have dumb utilities that charge high rates if you use more than 1000kwh, which most EV owners certainly do.