Get a used DC Level 4 XL 18" they're about $350 in decent condition used. Like other guy said you'll need a new box and amplifier anyways if you're expecting box, amplifier and subwoofer for $350 you'll need to start limiting yourself majorly. Make a box for 50 and buy something cheap like a used AudioPipe 1500.1D for $100 or less. Get a Obsidian Audio 18" They're about $200 and will take around 1k-1.5k daily in the right box with the right electrical. Then again you could just get this deal which isn't bad but you won't see any true potential from that subwoofer with that box and amplifier, the configuration I just listed would probably be louder.