I think the problem is there's no guarantee that any artist / designer / typographer will get paid for their work. Any artist worth their salt would charge at least £200 / $300 (ish) for a job like this (a guaranteed sum, rather than a 'as long as no one does better than you' kind of thing).

Barring Acorn, everything submitted in this thread has been a sub standard in comparison to the first two examples you posted (which, whilst beautiful, obviously aren't quite what you're looking for). You'd be best contacting a designer you like and offering them the sum through escrow rather than trying to turn it into a competition - which most artists see as just an excuse to get as much work as possible for free. The final week could pass and you could easily decide you don't like any of the work that each person has put X-amount of hours in to develop and you could just log off and never return.

Obviously i'm not accusing you of this but there's an element of trust to a competition like this that professionals wont buy (but hobbyists and students would - leading to the sub-standard attempts).