A diesel genny all the way. The power companies would charge an arm and a leg, not just for the power but also the installations outlay.
I'd recommend a HushGen made by I think it's FG Wilson. Very reliable, quiet (almost silent) and seems quite efficient too. A lotta metal for the money, last time I brought one (2006) t'was £2.5k for an ex-rental, fully serviced and maintained and re-engined in 2003, so practically brand new where it mattered for a 30kVA 120amp (40a/phase) beastie.