Chrome Extension - on page calculations

We need to develop a Chrome Extension that can make calculations with on page data on particular website. Website has table embedded on the page with multiple columns. Data in the table refreshes every minute, most likely using AJAX or Java. Extension will need to add 2-3 columns with results from simple data calculations for each row of data. For ex. divide number in one cell by sum of numbers in other three cells. We were able to inject additional columns using Inspect Element in Chrome and they stayed on page refresh. We can provide page source code on request. Results in additional columns need to be color coded depending on the range, for ex: from 1 to 1.9 - red, from 2.0 to 2.5 yellow, etc In future, extension Settings interface will be required to set range and colors. Developer need to be familiar with monthly payment monetizing options for Chrome Extensions.