How to add new features

Hi,

I have a functional wordpress ecommerce website. Since this concept didn’t take off I am now looking to do something else in ecommerce. I am planning to add an auction feature. The auction itself will be a bit dynamic in nature. My question is – how easy or difficult is it to add non-standard features to an already functional site? My motive is to keep my costs at a minimum. So instead of getting someone to develop another ecommerce site from beginning I am wondering if i can find some one to code additional features into my existing code.