Ask HN: How does a developer find a digital artist?

I am a CS student currently working full time and I develop some side projects for my entertainment. One area that could really use attention is graphics design / art. For example, I am looking to slap together a wireframe of a project to make a proposal, but it looks quite bare, so I'd really like to get some mock-up art or basic logo design done.

As I'm not a digital artist, nor do I have the time to try some basic art myself, how would you recommend finding someone to offer concept art, keeping in mind these constraints:

- This is not a full-time paid position, just a side-project

- I am a college student with not much money to spare

My first thought was to use sites where one posts a request for art and provides a budget, and artists across the internet can "bid" on the project by submitting samples. However, these can get quite pricey (see constraint above). What would be a great scenario is having fellow students contribute art for the sake of putting it on a portfolio, and, in the case of larger side-projects, I could offer % stake in the project, granted that the payout would likely be minimal to none. Any recommendations?