Thinking market, industry, referrals... it's important to look beyond the big networks, sometimes drill down if you're a more specialized biz. Other places to check are other niche networks and forums, being careful as most of these are protective of their communities (meaning no sales pitches). As you're considering 'bang for the buck' you're spot-on about the small business owner's strengths (and weaknesses); this has to be concentrated where they'll actually spend the time to see any returns. Words, pictures, videos - it's what they can do and what they're target audiences respond to the most. 

And as always, once you've found the right network remember: be social. People connect w/ fun, helpful people much more than they do w/ someone who only posts things to sell them something. FWIW.