Sensitivity Analysis - rank the input variable by importance

In the attached file, I have results of 100 simulations. I have six input variables (x1..x6) and a response value (Y). For these 100 simulations, I want to know which is the most important variable, which is the next most important variable, etc. Basically, calculate the importance factor. Use any simple technique that is well documented (Gradient boosting, Saltelli, Sobol) and provide the reference. My preference is that you do that all in Excel VBA. My second preference is to do it in R. Please suggest another alternative software, if it provides a simple solution. My budget is approx. $50, willing to pay higher for a good, simple solution.