I used a design contest site (99designs) a little while ago and now really regret it. The design work was great but supporting this model means being complicit in moving the industry towards a terrible set of circumstances for the designers themselves.

How about finding someone's portfolio you like on Dribbble[0] and working with them directly? There's a lot of cool work on display over there and you get to support someone's craft if you go down this route.

[0] - https://dribbble.com/