I think the cheapest would be an SKS. You can get an "excellent" condition Yugo SKS from Centerfiresystems for $199. It has a wood stock but meets the "ugly, evil" requirements because it comes with the bayonet and a grenade launcher attached.
For $50, you can get a black folding stock to complete the look you are looking for and definitely have a fun rifle capable of your accuracy requirements.
this stock
