Do you know of any software or website which generates a "renting versus buying" analysis for a prospect?

I gave someone an Excel sheet with my calculations. He thinks I may be overlooking something in the analysis but can't point to anything. So, I'd like to show him an analysis prepared by software, or an outside spreadsheet, so he can verify that it produces the same calculations and results.

You can check the calculator on my website provided by Point2, it does a rent vs buy analysis.

Anyone know of a software program that allows you to vary the values input for a series of years for appreciation, return on investment of potential down payment funds, rental rates, income tax rates, etc? So that everything is not calculated as a fixed constant for the period of comparison.