what subs do i need for std cab truck?

Hi, I've started the investigation on what to put behind the seat of my 1986 nissan hardbody (D21) std cab truck, I haven't been into audio in a while so I don't know whats new & clean but efficient for my wants & needs. I need the sub or subs 12's or smaller to be $200 each or less. I need the box volume to be no more then 2 cubic foot per side. Now for what I want (yay!), cab flex is fine, if I bust a window thats fine although it's been about 10 years lol. I want something with extremely low frequency possibilities (I'll probably do the figures for a port as well). I'm trying to keep the power useage @ 500wrms or less, but I'll see where this go's. I'm feeling around to see what everyone else has & compare numbers when I get idea's rolling....Many Thanks In Advance!

2cubic ft per side. so a total of 4 cubic ft.. you have room for a 4 cubic ft enclosure behind a std cab pickup?ac delco am radio and sparkomatic 40 watt sound exploder