piece together your own kit.
318s have the battery in the back also right?
If so, DO NOT BUY A KIT.
You dont need such a long power wire unless you plan on putting ur amp up front.
Get a good set of RCAs ~$15-50
Goto a Car Audio place, and buy your power wire by the feet. (Bulk)
Depending on where you wanna put ur amp, i'd say about 4f is good.
Get something 8gauge or less. Remember lower the gauge, thicker the wire.
4ft (+) Wire $10-30.
4ft (-) Wire $10-30.
Buy a fuse holder $10-20.
Some connectors $10
then you just need a remote wire, and some speaker wire for the subs.
those prices are on the very high side, you can find stuff for way less if you know where to look.