Study study study. Watch videos on YouTube, lots of them, to build a box. It sounds like your very new to this world so you need to under stand how important each component of a system is. Shop around in the for sale forums over the next couple weeks and for 500 you could pick up a decent sub and amp combo. You also need wires(power, ground, and remote) rca cables, a head unit, the box ( 1/4 the price of pre fabricated if you build it yourself) and a capacitor or capbatt if you feel like your battery won't cut it. Do your homework and you'll have a killer system