Most freelancers will charge more than what you're offering for what you're asking. Especially since they know this isn't just going on one item, and in-fact, on multiple. They will see multiple profit opportunities and view 450 in merchandice as a rather low offer.
If this were presented as some sort of contest however like 'Design the Next MameRoom Logo and win an Arcade System!' then your offer would be acceptable.
I have no doubt that some people will submit art, and hope that you get what you are looking for. I would personally suggest finding a freelancer, or even professional design group that gauruntees low consultation fees.
And the consultation fee should always, and I do mean always include a discussion between you and the designer about what you want, and a draft or sample or two of how they interpreted that, so you're not paying out the rear end over something you don't want.
I wish you the best of luck in finding the art and design that best represents your product line.