I am doing a 1.5m x 6m single story extension with quotes of 35 to 55k with most about 45k. Ours has no access & all has to be dug by hand mind. Even so. Increased meterage + 2 storey you'd have to double it. Ball park 70 to 110k. Doubt you'll get any change out of 90 to 100k if guessing (Inc VAT)