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 $100k to design NEXT's logo
Gief link to your portfolio. I'm professional from a very different field, so my understanding of the graphical design is limited. Please forgive me my ignorance but it is very hard for me to accept 100,000$ logos (for example Moscow Metro logo cost $3,000,000+ and it keeps me stunned by this incredible amount). Somewhere in my mind I think that marketing effect from the sole fact of than amount of money spent is bigger than from actual logo. (Question remains what kind of marketing required for transport that is already serving ~30 000 000 passangers/day)