i been running v8 3.9 efi on gas and it cost £26 (to fill gas tanks)empty to full,
and that took me from dudley west midlands to huddersfield west yorks at 90 with some gas left over i was happy with that (gas @ 60.9 ppl)
i am about to fit a 3.9 efi auto on gas in my 110 (g reg) currently 200 auto
i recommend it and should be worth it for the fun afterwards if economy isn't a issue
mine is a toy