Agreed, no generator is going to be cost effective compared to commercial power. A small generator (say 20Kw or less) would cost many times more per Kw/Hr than commercial power, mostly because of efficiencies of scale.
Look at your bill. I'm guessing your basic charge is less than 10$, the rest being per kwh charges. Generated power will cost way more per kwh. You do the math
Listen to these people.
My home meter costs around $5 a month.
I have a 1MW diesel generator where I work, and delivered power is STILL around 20% cheaper than self-generated power, and this is in a part of the country where electric rates are as high as it gets, and isn't even adding in any operating costs beyond fuel (such as oil, service, capital costs of the required infrastructure, etc).
I've done the math here, to consider if self-generating would save us a little on the "demand" portion of our bill, by dropping the peak from the hottest days of the year, but the difference was still negligible (and a residential customer doesn't have a demand charge).
At home, my gasoline generator (I have a 5kW, and a 1kW inverter unit) power costs something like 400% of the cost of utility power when you consider the cost of fuel (ok, gasoline prices on Long Island are always above the national average, but not by more than 15%). It isn't even close.
These are best case scenarios. Worst case, you have a generator that's way oversized for your load, and your fuel costs per kW may double.
If a connection to the grid is available on-site, you simply cannot scale up your own generating to match the cost of power from the power company.
Or go at it backwards, a 3000 watt generator with 4 gallon tank will run 8 hours on half load (1500 watts x 8 is 12 kilowatts per tank, a tank is $16, shore power is $1.92). This is also true for "car power" as far as charging your cell phone etc.
