Social Media by setting up useful groups related you your niche - Now, firstly, I know you're looking for free, however, setting up a page and inviting friends and family is a start, but you have to be proactive. Say your product is for example - bird houses - well then, it makes sense to join some various bird fancier groups with as many followers and as possible and all kinds of other related bird groups. Like bird watchers or specific bird groups like parrots (chances are their users will like birds in general) - Some groups will let you post without moderation others will require the admin to allow the post - I've found it good form to ask the admin if you can post to his/her group. Maybe you could offer the group a special discount - admins of large groups are more likely to say yes if they're able to pass something on to their members and will probably endorse your post - others may ask a fee -
My second point is this - Instagram campaigns start from £1 GBP
Facebook from £4
Basically it's bird feed :)
Remember £4 for "targeted" advertising - I started an Instagram account two or three weeks ago and have almost 300 followers just for posting occasional pictures I find on Facebook groups for my niche. I have 50 Facebook page like/follows doing the same within the week and now I'm getting people liking daily who are just finding my page however people find pages (however, the more followers you get the more you'll get through those followers)
Add Hash Tags to Posts. On all the Social Networks, tags help people find content. Add them you tour main site.
Follow 4 Follow pages are another, I as an experiment I set up google + and got 45 follows in an hour, then I set up a google group doing my own f4f community and invited all the people who had followed me. Then I made a couple of quick images in Gimp (Open Source Imaging Software Similar to Photoshop) advertising my community and started asking people to invite their friends, posted my images in other f4f groups - now I got a community that has 40 followers for 10 minutes effort
Good luck - Sorry for the Typo's, I've corrected a few!