Here are my two solutions! I went with a more dynamic/scalable method for Method 1, and then decided to do a single tool solution for Method 2 using the Formula tool.
Involved some thought!
One was to create a simple formula - then reorder - second way was to transpose the data and join the cost and tax side-by-side then calculate the rate and crosstab/dynamic replace the field headers/names. Used expect equal to verify that both matched the solution.