I had a problem a bit like this a while back: I had (and still have) a small side business, and needed a shopping cart for it. I looked around at open-source solutions like osCommerce and Magento and decided they all sucked, especially for my use-case (I have a small number of products for sale, each with a lot of documentation, instructions, illustrations, etc., not a giant retail site with hundreds or thousands of products with a minimal description for each). I tried, but these programs were all such huge monoliths that it was too impractical to strip them down to the minimalistic code I wanted to run, nor did I want to use a database (I run on a small, cheap, slow webserver and want to keep my page-load times decent). I ended up finding a somewhat broken but minimalistic shopping cart program in PHP, and learned enough PHP to fix it up and customize it for my site. That program is now abandonware, but my heavily modified version is working great on my site, and does just what I need: gives me a simple but functional shopping cart and is very fast, and if I need to make more changes is easy to modify because it's not a giant mess of tens of thousands of lines of code in hundreds of source files with zero comments (I'm looking at you, Magento...).