First step for any ecommerce business - setup google product listing ads, it will give you immediate access to at least somewhat qualified traffic
When you say "minimal cost" the alarm bells start ringing, you need to have a decent marketing budget especially at launch because its going to take some time and its going to burn some $$$ before you get the marketing right
Etsy, instagram, facebook and pinterest are all useful too as they're visual mediums but as other posters have pointed out, you need to test and see what works for you.
If you're new to this, perry marshalls 8020 marketing book is a good place to get a better understanding of online marketing
