By Susan Edmunds of RNZ Who has the most disposable income in the country? RNZ has crunched the data to look at which areas in New Zealand are left with the most in their bank accounts after they've covered the essentials. The exercise is far from definitive, and everyone's individual circumstances will be different, but it gives an idea of the pressures in various regions. Looking initially at the main centres, we've started with Infometrics' estimates for the year to December for mean household incomes in each area. We've deducted tax as if one person was earning that amount, for simplicity's sake. Then we've deducted the average rates bill for that area, the cost of servicing a mortgage at 80 percent of the value of the area's typical home according to Cotality, the median cost of house insurance according to Consumer, a typical food spend according to Stats NZ, and the average local power bill.…