Civic GX

I've been running some numbers on the Civic GX and... they don't look
good. I was considering purchasing one and a Phill so I could refuel
the car at home. But looking at last month's natural gas bill, this
seems like an expensive proposition. Here's what I did.

My last natural gas bill was $50.31 for 21.6 therms. So I first
converted the therms to the energy equivalent in gallons of gasoline.
I realize this is sort of sketchy, but it's the best I could come up
with; please let me know if you know of a better way to compare "apples
to apples".

21.6 therms * (100,000 BTUs / therm) * (1 gallon of gasoline / 114,100
BTUs) = 18.93 "gasoline gallons equivalent"

(Funny, I was just reviewing the factor-label method with my niece...
)

But if that's correct, then I paid 50.31 / 17.42 = $2.66 per "gasoline
gallon equivalent". So then I thought, "OK, but what about
efficiency?" Still, the Civic GX only gets 30/34 miles per "gallon
gasoline equivalent". That makes for some pretty expensive
transportation.

Has anyone else run a similar analysis? And, if so, how do our results
match up?

Thanks in advance,
Bill