This is an interesting peak into the world of Instagram-as-a-business-tool, covering costs and tools of "influencers". On hipster-friendly lifestyle content that should be added to the main topic:
Another difficulty was that I’d been told to post at least one piece of “lifestyle content”—that is, a picture of something other than myself—every day. In general, pictures of people get more likes than anything else, but the idea was to create a sense of variety and to avoid boring my new audience. [ ... ] Alexander introduced me to Alisha Siegel, a wedding photographer by trade who also sells stock images to influencers. Siegel could offer me as many perfectly framed lattes, hipster hotel lobbies, and urban sunsets as I wanted. I bought 20 for $400, which brought my total tab for photography services to $2,000.
On the cost of sponsored posts:
By the end of Week Two, I’d reached 600 followers, or a threefold increase. Saynt told me he thought that if I kept it up, I could be at 10,000 by the end of the year, which would be enough to command maybe $100 per sponsored post.
For a completely different angle also see Wired's story Like. Flirt. Ghost: A Journey Into the Social Media Lives of Teens — it's amazing how differently social media is used by those two audiences.