I have been playing with the 2% rule in a spreadsheet. What I came up with is what I call the net income as a percentage of cost basis. First, I include renovation costs and purchase cost as the cost basis. Then I do a quick analysis of expenses, real estate taxes, insurance, management, vacancies, repairs, inspections. Then you simply divide the net income by the rent. This gives me the net income as percentage of cost basis.
My spreadsheet also shows me the projected rehab costs, the cost basis, (which is the purchase price plus the rehab), cost basis as a percentage of AVR (like for the 70% rule), equity, (which is simply the after repair value minus the cost basis), and net income per month. Now I have a sheet that I can use to evaluate a property.
Then have a sheet called comparisons that I link the metrics of the property evaluation sheets of the individual properties that I am considering and I have a metric that I can compare one property to another and see which one would perform better per dollar invested.