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
I a good logo does more then people seem to understand and people should be willing to pay for the best logo possible if they want people to even look at there coin/product.