I'm not a graphic designer but I think you are seriously underestimating what this kind of work costs. If you want pro work, you gotta pay a pro price. People will invest time and talent for a
chance at winning .2btc, that's the kind of work you're gonna get. If .2 is the budget, then straight up hire a freelancer for a couple of hours instead of running a contest. .2 is insulting for those who actually went to school to learn the craft.
I'm a designer and as a freelancer I generally charge $500 USD for a logo for a small business, logos I tend to not charge by the hour and prefer flat fees because a good logo may take anywhere from 3 hours of work to 30.
Naturally of course corporate work is a whole different ball game. Steve Jobs paid Paul Rand $100k to design NEXT's logo