Opencart: modify Google Product Feed extension to add a single line of code for each product.

I have an opencart based website and i have installed an extension to connect with Google merchant through shopping feed. Everything is working fine with the extension and the shopping feed is working as it should. What i want to do is i want to include a line of code in the shopping feed for each individual product. The code is essentially "g:shipping" followed by the shipping cost for that individual product which i will provide. So i what i want created is, in the product edit page in opencart, currently i have a tab for google feed (which is the extension) in the tab i would like to add an option field to add "g:shipping" for the product. You will need to modify the VQMOD in order to do this. I hope to work with someone who has had proven experience writing VQMOD and Opencart projects. My budget is limited so i will only consider a competitive priced proposal. Please consider asking questions in regards to the project as dont usually respond to template responses. I also prefer to work with the coder directly and not studio's or project managers or teams. Looking forward to working with one of you.