Values for the Calculators

[Account Closed]

I'm trying to do some calculations using the calculators (in particular, the BP Wholesaling calculator for rental properties). I'm wondering, though, how to find the estimates for the expense calculations. I'd like to find some good numbers for sewage, water, garbage, and homeowner's insurance. What do you do to calculate (or look up) average values for an area? Do you find it varies in different parts of town? High water usage should lead to high sewage cost, but then...what do I put in the calculator? 

Do most people simply use the 50% rule and call it a day? Is that conservative enough? 

Is there a set of tables you know of (or even created yourself) to figure out the average cost of utilities in your area? At the end of the day, though, do you find that your calculations come close to reality?