my cats probably cost approx 30-35 each month to feed whereas my 2 dogs cost about 40 each month...they just get dried so that keeps cost down. If they ate wet food the price would be rediculous.
I suppose dog insurances does cost more than cat and generally vets bills are normally slightly if not abit more due to size difference and needing stronger or more meds etc.
mind you depends which types of dogs, obviously smaller dogs will be much and such i'd have thought, i have 2 greyhounds and 3 cats.