I don't enter these contests so I will offer my advice to you.
Put a fixed price. Or designers have zero idea what you're looking for. Do you want a super high class design worth a grand? Do you want a quick 50 dollar piece of shit?
Remember ... designers wont put the time into something they aren't sure they can win. Bidding based on a portfolio is easy. Actually putting 8 hours into a logo and then just hoping it met the criteria is not.
Fix your price, and explain what direction you want. You will get better results from the entrants
Good luck!