I understand people search places like Deviant Art, Fiver, and other bidding sites due to budget, but these are not the places to actually get decent work. No self-respecting professional designer would be peddling their wares anywhere near these places. A quick Google search will show you designers in your area, freelancers will be cheaper than agencies and printers will offer services cheaper than freelancers.
$100 obviously isn't much of a budget for something that should really cost in excess of $500 but you can always appeal to professional designers to see whether they will take you on as a low-budget client - it will limit your options but you'll still get professional work. Otherwise you might look at
pre-made covers.