Best non-profit ecommerce solution?

Hello!
I'm volunteering to redesign a website for a fair trade organization (proceeds help craftsman in underdeveloped countries), but they want to add a shopping cart to their site within the next year. I prefer to code, but the volunteers get scared when they hear HTML used in a sentence, so I need a simple solution I can turn over to them. I've been researching different ecommerce solutions and have read some of the threads on this forum, but there are so many options that I feel completely lost. Could anyone suggest an ecommerce solution that:

• could be updated by someone with little or no web experience (most important feature!)
  
• allows back-end editing
• has responsive templates (or lets the designer build templates)
• costs less than $30 a month?

Right now they like WIX, but I'm all about responsive design, and WIX doesn't seem to have responsive templates. I've seen some threads on storenvy and prestashop, but I'm worried about going free or super cheap.
I feel pretty in the dark right now, so any suggestions would be greatly appreciated!
Thanks in advance!

 

Try with advanced free open source shopping cart software like zeuscart to create your store.
http://zeuscart.com