I'm paying about $67 per month (on average) now for our utility company supplied electricity, If I could make my own electricity using only 2.5 gallons of propane per day (on average), then for about an extra
$100 per month I could take my house off grid.
This is precisely what some of the Mennonites and less strict Amish in my general area are doing. I shop at a Mennonite/Amish bulk foods store that generates all of its electricity with generators (having both a propane primary, and an oil back-up generator).
$167/month ~= $5.50/day
$5.50/day / 2.5 gal propane per day = $2.20 per gallon for propane (which sounds about right)
This of course assumes that the generator will last forever and not cost one dime in maintenance and upkeep, and that the price of propane will never increase.